No, you don't have to run out and buy some expensive solvent to remove the glue.
Just take your hand held Hair Dryer and turn it on, allow it to heat up for about 5 minutes. If you have and extension cord plug it into that, so you can take the Hair dyer to the bumper sticker. You will need to close in on the sticker, you want to heat it up, not melt it. So pay attention. Don't let it bubble up...
You will need to move the hair dyer up and down from side to side along the bumper sticker.(Feel the sticker with your hand to make sure it is nice and hot.
When you have heated the bumper sticker pick a place to peel it away.
If all has gone well it should peel right of.
If you have a very old bumper sticker it may try to give you a hard time peel as far as it will peel without forcing. (never, never force it).
Turn the hair dyer back on and point it and the stubborn spot keep feel to make sure it hot but mot bubbling. Remember no forcing just Keep repeating the process.
This tip works because the glue they use on bumper stickers are responsive to heat.
If you know a better way please share it with us..