So lets say you are a city.  As with many American cities, you have a small homeless problem.  All your highways have feeder roads, so there are lots of underpasses with traffic lights - what a perfect place to live and work if you are a homeless person (and by "work" I mean hold up a "United Negro Pizza Fund" sign and a cup). 

What do you do, city? Well, you want to make it clear to the homeless that they should not be living under the overpasses.  But you can't put up a bunch of signs that say "Go back to New Orleans", right?

Perfect!

They aren't homeless.  They are "campers".  And they aren't living under the overpasses to keep out of the sun and the rain.  They are "camping overnight" - which is clearly prohibited by the signs.

Oh, and this?

That's just "camping equipment".  Glad we cleared that up.