My dad was KBKF9922, and used the handle "Firebear" as he was a fire police officer with a volunteer fire company in our township in PA.
On the AM channels, most users have a made up handle. The FCC does encourage users to use a callsign of sorts. Under rule 17, one of the suggestions is to use the K prefix, your initials, and your residence ZIP code. Mine then would be KJHG85345. I'm not aware of any users who actually follow that suggestion.
https://www.fcc.gov/encyclopedia/citizens-band-cb-service
SSB users may belong to a local or regional club, and are issued a 'callsign' through that club. That callsign of course carries no legal weight as an FCC issued callsign would.
Years ago, I acquired the callsign SSB-83T through the SSB Network. I believe that that national group no longer exists.
John
Peoria, AZ