Part VIII. Post-Strike Striking Chamber Mishaps:

Ejection Damage:

Crenellated rim

Definition: Reeding prolongations generated as the newly-struck coin is pushed up and out of the collar. The reeding extensions always point toward the face struck by the anvil die. They stick up vertically from the junction between the design rim and the edge, forming set of sharp prongs that look like a picket fence or the battlements of a castle. It’s not clear why crenellations form or why they occur so rarely.

Crenellations appear on the reverse rim of this 1976-D quarter dollar.