GooGone is what I use. Our TT dealer placed 4 (yes 4) hard plastic dealer name plates as advertising basically on all corners of our TT. First mod I did was to remove 2 of them, left the other 2 because the dealer was great to work with so I dont mind a little advertising for them.
*Currently trailer-less but shopping
07' GMC Envoy w/ P2 controller (current TV)
88' Chevy K5 Blazer (soon-to-be TV)
74' VW Superbeetle (1303)