Uh, I disagree with the Mp "Only seen them three times" statement, which is probably true in your experience.
But, I've seen them MANY times and watched tow trucks come with them (2001?). They are not nice after a few weeks of asking people to leave.
If you take the time to get a pass it is no problem. I've had a pass for several years and just tell them it's in my window. Also, you must carry the other pass on your person. Last year they had their M-16's (M4A1's?) with them! Scary bunch of dudes with those red berets and no smiles if you have no pass. But cool if you do.
And, yes I have seen them politely ask people to leave many times as well, but why take the risk of being hassled? They can impound you and your vehicle. Get a pass. I'll leave that up to you, cuz actually, less is more down there...