From an add for replacement ones:
"These emblems (badges) are attached with pins on the back of the emblems being pushed through cir-clips inserted into the slots on the gas tank. If your gas tank has been body filled and painted, the pins can be clipped off (the emblem metal is very soft) so the emblems can be attached with 2-sided automotive moulding tape available from any hardware store."
I've attached a picture of the alternator cover post & clip (post on right has the clip on it, post on the left is bare), which I think is the same thing. I've naver had them off, so hopefully someone else will verify all of this.