That hasn't been my experience. I've seen some that use public key crypto, but mostly they do not because even the smallest secure cryptosystems have signature

That hasn't been my experience. I've seen some that use public key crypto, but mostly they do not because even the smallest secure cryptosystems have signatures on the order of at least 20 bytes (and more conventional choices more like 256-bit ECDSA... 64 bytes)-- which, after conversion to typeable characters, are a bit unwieldy.