Household "GOOP" adhesive works very well for adhering automotive trim pieces and it dries clear. Automotive "GOOP" is also available, but I don't think there is any difference from the household "GOOP" other than the price.
------------------ Now new owner of a Black TTop 88 Fiero GT and owner of a Silver 88 Fiero GT. Also a second time owner of an 85 Fiero GT. Bought my first fully loaded Red Fiero GT new in 1985. Fiero's are Fabulous, Fix'em and have Fun! Note, Avatar picture is Mr. Bean (not me, ha ha).
I have had very good luck utilizing the double sided 3M trim tape for emblems. So far more than five years with zero issues. That is how the original emblems and letters were attached and some of mine were installed for more than 20 years until they were removed for paint and/or restoration.
[This message has been edited by hnthomps (edited 07-04-2012).]
Double sided 3M trim tape for emblems is more than enough. You don't want something too hard as sooner than later you may need to put a new one to keep looking nice. After 5 yrs I needed a new one for the new paint job and the 3m was easy to remove.