What's an "ear tip"?

Ear-tipping is a method of identifying cats in a colony that have already been spayed/neutered and vaccinated. When the cat is under anesthesia for the spay/neuter surgery, the tip of the left ear is surgically removed. (See photo below.)

This doesn't hurt the cat or affect his hearing, and makes it possible to visually identify all cats in a colony that have been TNRed. Ear tips are required for TNRed feral cats to be in compliance with Baltimore City's TNR law.