I need to re-attach a mid 80's Trek headbadge after a new paint job but I don't know what adhesive/technique to use. How do I do it? - thanks.

I use double sided foam tape:

https://www.vikingtapes.co.uk/Tapes/D...plate_tape.htm

If it was riveted on previously I make fake rivet heads by cutting off a couple of old spoke heads and gluing them back in the holes

I've used shoe goo on several, never had a problem.

Thanks.

There are proper head badge attachment screws, or rivets actually. These little rivets have an enormously aggressive thread and hold pretty darn good. In industry, they are used to attach information or name plates to electric motors, pumps and the like.

This page shows an example of what you seek. Make sure that you get stainless steel units. The others will rust as you are installing them.

My favorite adhesive in the world, and what I use for headbadges.

Slightly off topic but related - what is the best way to get a factory glued badge off? Dental floss?

I made a mistake and used the 2 part expoxy on mine. Which is bad in the future if I ever want to change the color of my powerdoated bike. I have NO idea how to remove it.

Double sided tape is what the manufacturers use to attach badges to car bodies these days. I use a piece of string to remove them.

The badge on the one Trek that I've had was not riveted.