Take a length of fishing line, tie each end around a wrench (you'll be holding on to the wrench instead of the line so you don't hurt your fingers when pulling the line). Use a sawing motion (pulling towards yourself) to get under the edge of the emblem with the fishing line, and slowly make your way all the way to the end of the emblem. The emblem will come off, but you'll still have a fair amount of adhesive left on the bike. Heat up the area slightly with a blow dryer, then soak with mineral spirits. With a bit of elbow grease, you'll be able to remove the adhesive. When you're done, clean off the tank, and polish her up!
Keep the shiny side up...

exactly, thank you. I have just said to me that if I also
found those of the tank, the motor bike would be even more beautiful in the American style of the "tourer"