Technically nothing, but legally it's just not allowed in the US (neither for FRS/GMRS, nor for ham radio operators, with very few exceptions).

Interesting, is speaking in a language that nobody else understands counts as "encrypted transmission"?

That’s what I mean. Isn’t any data the same as speech in general?

The phrase "criminal intent" comes to mind. No idea if anyone actually cares whether a signal is clearly understandable or not unless you're targeted for some reason.

the content of the speech is protected. you can say "fuck this guy" where this guy could be anyone.

but you can't legally send encrypted over the radio, since those protocols are restricted by the FCC.

You won't catch a charge for what you said, but you might get fined for misuse of the radio band. its the same way you can't spray paint a slogan on the front of someone's business -- the content is fine, but the medium is not.