Vacationers and tourists are targets in many areas. They have cameras, extra money, etc in their vehicles, are more lax in their situational awareness, less familiar with the areas about town.
Generally, it is wise to remove all signs that identify you as one, such as rental car info, vacation tags like the cg placards mentioned, cameras, cellphones, electronic items, bank envelopes, vacation supplies, tourist brochures, and the like.
Some of us camp to escape daily stresses. It's nice to be anonymous once in a while.
Besides, the question should be, "Why do they *need* to require you to display your info (most places use rsvp numbers anyways)" NOT why do you want to keep it private.
In America, we do not need to defend or justify our right to privacy, rather the entity who wants to take it must justify with a compelling reason. Otherwise, we may as well just give up and sell our flag to Iran :R
Too many forget the sacrifices made so we don't have to play "Show me your Papers" or "If you don't have anything to hide, you should let us...search/take/track/etc"
Paranoid? Nope, it's called vigilance and appreciation. ;)
