Thanks for the replys.
The reason I am asking is because I sold these to someone on ebay.
They did not pay for the item, they contacted me (after some time..) stating that they were contacted by St Louis Crystal and that they stated all genuine glasses were marked, and the glasses could therefore not be genuine. They then stated that St Louis Crystal would be starting a listing violation against my account. The person says they are awaiting a reply about there authenticity from St Louis.
Any more info, making the attribution more concrete would really be helpful.
Best Regards