Here's the response I received from the auctioneer of this item. As they say in Latin-speaking lands, caveat emptor:
It is not signed, but as you probably know, a great deal of the fine Murano glass is not signed. Our collector collected Murano for 20+ years and is considered an authority. They vetted out any questionable items so as not to taint the sale. They are certain, through their many years of research, that it is authentic. It was made in the late 1970's, based on the feel of his other items of that period, but the glass-maker is not identified.