but are normal plebs going to be arrested for having Signal on their phone or with a Meshtastic/Meshiliscious device?

Are you deliberately trying to be obtuse?

The “criminal encrypted communications device” - whatever the hell that actually is^1 - is the very small cherry on top of the firearms and whatever other investigative legwork needed to identify, locate, and then arrest these people.

So no, unless you’re also often nipping off in a taxi with a few guns to do a job for another crime group, I think you’ll be relatively safe fooling around with meshtastic.

^1 Maybe it’s one of those CrimPhones™ that had their security protections quietly broken in the last few years.