When i want something to stick FOREVER, I use what the Acquarium builders use - pure silicone glue (DOW Silicone I, NOT DAP and NOT DOW Silicone II - the useless stuff that cleans up with water and doesn't work, you want DOW Silicon I because that's the stuff that leaches acetic acid / vinegar and it lasts virtually forever.)
It's flexible and emits acid to help with the bonding process. It's also incredibly strong (a 1"x1" patch can probably hold 10 kilos ..)
Unlike JObst Brand, who coasts downhill too much, I find that head-tube flexion ruins my headsets, and so you will need a flexible glue to hold the badge securely as the head tube flexes. In my opinion, nothing beats pure silicone for strength and flexibility at the same time.
- Don Gillies
San Diego, CA, USA