Head badge
A head badge is a manufacturer's or brand logo affixed to the head tube of a bicycle.
Head badges may be made of metal or plastic, and they may be held in place with adhesive, screws, or rivets. Some are simply stickers, decals, or painted logos.
Head badges for a single brand may change from year to year or from model to model, as demonstrated by the variety of Trek head badges pictured in the gallery below.
The term head badge has also been used to describe other logos:
Araya
Beacon
Columbia
Diamondback
...
Wikipedia