I take it these are the red I labels, transfers, decals? If so, then the chances are the TS signature is an addition, and not necessarily contemporary, get my drift???? Having bought some boxed, and mint, unsigned, and genuine, (with Iittala receipt) myself I'd be suspicious. Having bought a labelled, TS initialled, allegedly unique, but stylistically correct paper-weight, which was later confirmed by Sarpaneva's family as a fake (ouch!!!) my advice is watch it.
Be careful, there are some "cads" out there, who think it fun to practise their limited range/knowledge of graffiti on glass, rather than underpasses, trains, bridges etc. Their financial gain is the motive.