How to recognize a stray cat that has been neutered

For the “Journée nationale de la stérilisation animale au Québec”, our team has sterilised stray cats from the Lac des Pins campground, in St-Antoine-Abbé. During the surgery of stray cats, veterinarians use two methods to identify that the cats have been neutered. The first one consists of ear-tipping of the left ear. The second method consists of using green tattoo ink on the surgical incisions of the females. These methods are commonly used in Trap-neuter-return programs.

https://en.wikipedia.org/wiki/Trap-neuter-return