Ames, Everybody has a call sign, and these are listed in databases and directories like a phone book. By law you must identify at beginning and end of conversation and every ten minutes. Theoretically, one could steal another’s call sign as an impostor, but you would get into big trouble, and be caught. Remember that you are on the open airwaves, and anybody can and does listen. It is not a place for private personal conversations. You can even listen without any license, just can’t transmit without a licence. The FCC monitors periodically, and any others listening who believed somebody was messing around would alert the authorities. Also, far away stations sound far away, fade in and out, and you would never confuse your next door neighbor with King Hussein.
I myself once transitted on a frequency I wasn’t supposed to be on by mistake, and got a citation (ticket) from the FCC monitoring all the way in Texas. (I was 13 at the time, and dial became miscalibrated, which is something you needed to check every so often, with older mechanical displays.) If you respond promptly and explain circumstances and what actions you have taken to insure it won’t reoccur, there is no fine or loss of privileges. However, if you ignore citation, then can get into trouble.
I don’t mean to scare you, as it is a pretty easy-going hobby, but deliberate messing around will eventually get one in trouble. There are some pranksters who try to jam and interfere with conversations and repeaters, and every club has members who know how to trace the source of interference and file reports.