I caught a few strays where I live a few weeks ago and brought them in to a shelter. Today two of them came back and their right tip of their ear was clipped. What does that mean?

It means they were spayed or nuetered, given their shots, and returned to the community. The ear tip helps other rescues know that these cats are already fixed. Feral cats don't often get adopted. This gets them back in their community, but unable to make more kitties.

Thanks Jim. I was kinda hoping they wouldn't be brought back. Someone in my neighborhood where I live is leaving poison out for strays.