Here are some videos about how to remove car signage. Make sure you watch all videos so you will get all tips and tricks to do it properly.
This guy using heatgun on very old signage. Watch you fingers while doing this! Safety first!
This one is bit longer but also using heat gun.
and this one is shortest
and last one using toffie wheel. You can get one on ebay or amazon whatever you prefer.
So after about 15 minutes you should have idea how to remove your ones. Cheers