In the US it should soak off. Soak the stamp in water and be patient. After a few minutes, the gum is supposed to dissolve allowing it to be removed. Don't rush, or you will ruin the stamp.
to get tape off copper you need to use a heat gun you can get them from your hardware store for about $10-$40. Some copper stains but don't worry it won't harm it. thank and see ya
If the adhesive is still sticky, an artist's kneaded rubber eraser should remove most of it. Dab/rub it gently at first to remove as much of the surface adhesive as you can, then with more pressure...
There is a solution that you can get at Home Depot or Lowes called GOOF OFF. This will remove your paint though. Hopefully the adhessive is on your windows or bumper.