WD 40 test in a small area first.......also try a little heat from a hair dryer.
+1 WD40 is my go-to as well for sticker gunk removal but I've never tried it on wood (It's great for metal and plastic). I agree with the "test first" advice. I'd take the pickguard off and test a spot underneath it. If it doesn't take off the paint or make stain, you should be good.