in view of the indistinct details in the original pix., and to try and avoid confusion - attached are some pix showing saw tooth decoration on facet cut stems of drinking glasses - one being a C19 sherry and the other a C20 hock.
For obvious reasons this sort of decoration can only be applied to what Nigel describes correctly as 'flat facet cut and polished neck' - sometimes called flat flutes - and the marks are placed on the 'arris' (the sharp intersection between two flat surfaces).
Elville says this decoration occured in the C18, but I can't see any examples in Ward Lloyd - he also says it is sometimes described at 'notched decoration'.
I'd also agree with Nigel's proposal that this piece is possibly of later manufacture than I'd thought originally.
P.S. If anyone does have Andy McConnell's book which they no longer require - give me a shout please