Another interesting link.
If it is a copy it seems to be a good one (although we then probably have to call it a "fake" instead of a copy)
With regards to the clear glass it seems to be different to what is mentioned there. Looking at the base the clear glass is not in the middle of the colored glass but on the inside and (at least on the base) the outside.
The signature is not a very reliable indicator but it's not an obvious fake one. Size and location look good, also the fact that it's not immediately spotted just by looking at it.
The area behind the desing is something we cannot check. It's just too small. From how far we can feel it's all smooth.