This is 100% absolutely not Steuben.
Their colored glass production stopped (for the most part) in 1932. Some special order color work was done for several years after that, but their direction was to produce clear glass in a Corning developed product referred to as 10M. Corning purchased Steuben in 1918, but Carder remained artistic director until 1932.
Steuben never produced a piece in this form. They also never produced an underside that looked that way.....
IMO the form of this piece would easily date the piece to post 1950 in which case if Steuben it would have to be clear. Their last recorded sale of colored glass by special order was in 1943.
Steuben used their name in signatures. They never used initials in place of the company name.
When they used the company name:
they used a Fleur-de-lis acid stamp with the Steuben name in it.
they used an acid stamp "STEUBEN" in block letters.
they used an engraved Steuben also.
they also used an embossed paper label which had the Fleur-de-lis with the company name.
There are other forms of signatures without their company name, such as "Aurene" with a shape number.
Hope this helps....
Personally, It has a Scandinavian feel of the 70's to me.....
Craig