There was some sculptural pieces like this in the 80's and I think you can see some examples on the Seguso web site. Signatures on the bottom mean little these days as a lot of ebayers think it is smart to disfigure glass with phoney signatures. Archimede Seguso only signed his very significant pieces personally in the early days, most of these are in collections or museums. There are some out there with a small neat signature most probably by an apprentice and these are also considered genuine and I have one myself also with label. This is most probably what ejean has.
Having said this, the seller offering this piece appears to be a genuine dealer. They also have a pyramid for sale that is claimed as A.Seguso also, so who knows. I am not a fan of these geometric shapes as I think they will be too easy to replicate later.