As a collector who cut his teeth on unidentified individually hand-blown glass that was unsigned. At the time the market was dominated by Lalique, Schneider, GallÃ© and other French designers. Collectors of British art glass were almost non-existant and virtually nothing was documented. Manley was about the only relevant work in that period.
I enjoyed not only learning about the glass but also the journey of discovery. Note, that I was at that time also a stamp collector and built a very specialised collection that required all sorts of tools and knowledge to identify the subtle differences. With no references to identify what was or was not Monart I also had to contend with the different makers of similar types of glass - in the process of which Nazeings history got brought to attention. Not having the luxury of signatures was thus a prime driver to really learning to understand the hallmarks of individual glassmakers. It became possible, eventually, to recognise Monart by touch alone. It was a fun 'party-trick' doing this with pieces I had never seen for other collectors. Also, I have to admit to looking down my nose at collectors who only collected signed glass, I used to make the same parallel with stamp collectors who only collected the basic values and did not care to go deeper into it. I no longer feel that way, it was part of my growng up in glass).
I am also aware that stores like John Lewis insist on glass being unmarked or even labelled.
Monart paperweights were normally labelled at the factory, though rarely coded. However, US collectors who bought their weights from Paul Jokelson got their weights without a Moncrieff label (They did have a PY cane) and it is not known if Jokelson insisted on no labels or removed them before distribution.
In my early days the only British glass with any following was Whitefriars Powell pieces or antique stem and cut glass. Glass artists were struggling and unable to get very good prices - few British glass artists have risen to major international prominence. Few of them signed their work either. I collected glass by a few Siddy Langley and Lindean Mill being the only ones I bought more than once. At that time Siddy was having to concentrate on bread and butter work and her 'art' was limited to when invited to exhibit. But only 3 galleries, Coleridges, Hayhurst and one in Bristol. Adam Aaronson was a sales assistant that I bought my first Lindean Mill from and I met him next when he had a gallery in Edinburgh after Coleridges closed. The discussion about signatures never occured in those days.
One of the main impact of the obsession with signatures is that they are an open invitation to fakers to reproduce the signature - the Chrism episode showed he did not care if the glass was scarce and valuable or cheap from a discount store. Many pieces were spoiled as a result.
One of the driving forces for glass manufacture for non-functional or decorative use is a succesful economy that leaves people with disposable income. Such an economy creates demand and desire, desire takes no account of wealth and this means that limited number of appealing and succesful designs are going to inspire reproduction and style following. Todays unique masters creation is tomorrows mass market vase and this allows more people to share in that original thinkers concept. Such an economy also faces increased wage demands as more people want to partake in the consumer process and to be able to enjoy the 'luxuries', this in turn leads to cost cutting in manufacture to meet the demand. Marking the glass is a labour intensive task and is often carried out by one or more persons in a factory. When trying to compete against cheaper imports the indiginous companies have to cut costs and expensive finishing is an obvious candidate.
Few collectors are studying and collecting current glass production. I am certainly guilty of not researching Strathearn while they were an active company and as a result much is lost. But Strathearn glass gives an indication of another issue with marking. Most Strathearn glass is marked with am impressed applied seal but in order to support that it was found neccesary to increase the thickness of the glass - increasing the cost. This is probably why many glassmakers did not use a similar approach. But even those seals were being ground down and a basal ring added in order to pass off as Monart. The accident of needing to thicken the glass resulted in a very different feel so it mostly hurts 'new' collectors. I would argue that you learn by your mistakes. The early period at Ysart Brohers glass saw the continuation of the Monart labelling approach, but this was very quickly replaced by an acid etched signature that was applied by 3 women using a brush. When times got harder and Vincent took Dunlop as a partner the signature was immediately replaced by a label of very similar design to that used by Dunlops Pirelli Glass. Indeed some Vasart was sold with only a Pirelli label on, but with made in Scotland instead of England. When Stuarts took of the Strathearn works it was used mainly as a decorating shop. Stuart Strathearn was marked by sandblasting over a stencil. While cheaper than most other methods of marking glass it is for collectors very dangerous because it is so easily copied. Acid etching needs a lot more skill, particular for well defined marks. The mixture of acid and flouride needs to be adjusted to each individual metal composition and I know one restorer who tried hard to duplicate such marks and failed.
There is one intriguing Monart piece smothered in signatures, was this done by Moncrieff's chemistry department to test mixes or is it the work of another restorer attempting forgery? (http://www.ysartglass.com/BaseLabel/Labelimage/MonSigEX1.jpg) a few more views are shown on this page http://www.ysartglass.com/BaseLabel/Labels.htm
(Some Monart was acid etched for export to USA, Australia, Canada and New Zealand). There is no provable example with an etched mark in the Monart exported to other countries.
Signatures and labels do form an interesting part of the in depth study of a factories output but have, in my opinion, little other value.
Each glassmaker has a right to decide for themselves if they wish to sign and this applies equally to artists.
An interesting discussion about a paperwight by Allan Scott in the paperweight forum http://www.glassmessages.com/index.php/topic,5696.0.html
the contributions of weight maker, Harry McKay and later in the thread attributed Martin Murray who facetted one of the weight. It transpires that the type of cutting used in this example is of the most complex nature and few have the skill to achieve this. Without the active involvement of Allan Scott, who made the lampwork and is viewed as the primary craftsmen, the contribution of Martin Murray would be lost to history. Then there is the polisher and any other assistants involved. Credit need to be given also to the other workers that contributed in some way to each work. Where do you stop?
Another signature focussed discussion in paperweights is about one signed with a script Schneider - this is leading down some circuitous paths and it is still not sure if this is a fake or an unknown Schneider!
There are plenty of hideous pieces of Lalique that are signed yet fetch a good price simply because of who they are by. I have owned some hideous Monart, because it was Monart, even if unsigned.
In summary, I would suggest that signatures are an interesting sub-topic for research but of no relevance to the collectability of a piece of glass.
Certainly collectors should not demand that glass be signed, mostly they are buying on the second market out of historical and fashion interest. They could go to still living craftsmen and pay them the value of the unsigned glass to have a signature added, although usually they just hand it over and say will you sign this piece please. Why on earth should the craftsmen do so? Flattery perhaps, usually they also get to buy a piece from the crafstmans own collection at the same time - do they pay the market value current, or just what the old guy asks for? I know that when I bought one piece from the Ysart family, I was generous paying ten or twenty times the pieces then value.