Futa vs Trap problem?

Story by Crossdipper

Hi all, I'm currently working on a a couple of stories that basically take place in a vagina-less town. It's very heavy on traps and futanari with balls and no vaginas and while I've done pretty good so far, I keep running into the same problem of how the characters can tell the difference between the two when they're mostly nude, but not when they're mostly clothed. I want to try and do this without involving something super odd, like different colored dicks or something. So basically the options I've thought of so far involve breast size(could be flatchested), penis size, some strange discoloration/mutation, or 'they just know'. All of which I'm not too fond of using.

I know it's my world and I don't need a why or how, but I feel like it would make the writing that much smoother.

How do you guys think I can pull this off?

Also, what do you guys and gals refer traps to in your stories if you happen to include them? Traps, crossdressers, femboys? And he or she?