Are pieces marked HGX from 1970, do you know? I have a set of glasses marked with this, which date to around that time.
As I said in the first post, I've one piece from 1980 marked HG80 - and this seems to be where this manner of signature stopped.
...as to unica they is always signed.
Unfortunately that's not always the case - I've four unique / limited production pieces without signature. Makes them difficult to sell on, I can tell you!