How can you tell the difference between 2 cats..one definately is a male and neutered...the other one I'm beginning to suspect is a female but I bought "it" a while ago as an adult. "it" or Dbub is kinda overweight so it's hard to tell...is there a surefire way to tell? My male cat doesn't have nipples, the other one does.
I have two male (neutered) cats and they both have nipples. Not as pronounced as my old female cat but they are there all the same. I'd take your cat to the vet just to be on the safe side. The nurse should be able to check for you! The other thing you could look for is a neutering scar. If it is a neutered male then, if you look just under his tail/bottom, you should see the remains of his manly bits. If there is nothing there then you've got yourself a girl.
Male and female cats have nipples just the same as male and female humans. As camille says they are not so pronounced as male animals but they are definitely there!