I'll restate the fact that its not that suprising its not signed at least in the U.S. as for multiple decades many really good studio vases/bowls that mimic past Imperial Art Glass, Durand Art Glass, etc. designs & treatments (after all these designs were not uncommon in the 1920s through early 30s in high end operations) have had the studio signatures carefully removed & are featured (although usually not on eBay) in many an on-line auction op that may feature as many as 100 auction houses. Those not familiar with the shapes/designs/treatments used can be taken in very easily & you can take a great studio vase from the 70s that cost less than $100 & turn it into a $700+ vase at auction with very little work. Maybe it doesn't occur in Europe, but over here its not uncommon at all as there are individuals that seek out & buy these older (and sometimes newer) studio vases/bowls on the secondary market, remove any trace of a signature, rebrand them as a product of any well known art glass op from the 20's to early 30s & put them on the block. Its been a cottage industry for decades.