3M double sided tape is what I normally use for emblems. If you need something thinner I have had good luck with the norton speedgrip structural adhesive but you need a special applicator gun and disposable tips for it so if you don't have any other use for it I would use the tape.
I used 3M two sided tape, a thin automotive grade, to put the "DODGE" letters back on my hood. Just clean the old emblems really good and use a razor blade to custom cut!