I have only seen a handful of signed pieces and all original. All signed Seguso Vetri d'Arte and never with Flavio Poli. Design & Arts had a gorgeous and huge Poli dolphin listed a few months back with a label and signed SVdA. Went out of my price range though.
I have also seen a plum and silver foil bowl/vase that was signed SVdA but didn't buy it due the silver foil. I only go for the gold ones. They are rare! And tip for telling a true one, they don't look as professional as these 2 signatures. They look rushed and loose.