Can anyone tell how to remove a decal from my trunk without damaging my paint?

if it's just a regular decal someone stuck on use a heatgun and peel it off a hair dryer might work too

3M adhesive remover, soak it and use a credit card or your license to kinda scrape it off

I used adhesive remover (goo gone I think), a heat gun and a light switch cover. Yep, a light switch cover. It had the perfect combination of stiffness, and a (relatively) soft, rounded edge.

Good luck.