Tattoo in my cats ear

Question
I just recently went to the SPCA and adopted a cat to be part of my family.  He was listed as a "Blue Russian mix" about a year and 7 months old.  They of course neutered him and sent him home with me and I've had him about 3 weeks now.  I just recently noticed that he had an "S" shaped tattoo in his right ear.  Can you tell me what or where this could have come from?

Answer
Sheila,

According to my rescue group sources, the "S" means neuterd or spayed.  With females, especially, it is not always easy to tell they have or have not been spayed, so they tattoo the ear, indicating the cat is fixed.

Best regards... Norm.