What does a spay scar look like?

For the past several months a female tortoise-colored cat from some unknown place in the neighborhood has been visiting our cat (who is neutered). She enjoys playing and sharing the menu with our cat. She is a nice kitty and is well cared for by someone, somewhere. We call her Tutti-Fruity. She doesn't wear a collar. She recently had a litter of three cute kittens and brought them to show to us. We didn't feed them so she took them back to her home.

Tutti was missing for about two weeks. She showed up today and has a small, thin scar, or fresh-looking slit about an inch long on her abdomen. We are wondering (and hoping) that her owners have had her spayed. Do you think this could be the remains of an incision left from a recent spaying?

Many thanks to everyone for any information.

We're tempted to have her spayed ourselves.

Sounds like a spay scar to me!