What is Ear Tipping?

An eartip is a quarter inch missing from the tip of the left ear.  It is the universal way we can tell if a cat has been spayed or neutered.  It doesn't hurt the cat, because it's done while they are under anesthesia for their surgery. It protects them from the unnecessary trauma of being trapped again, and makes everyone's  job easier as we can tell at a distance whether a cat needs to be trapped and spayed or neutered.

More info here.