Normative Signs: The Poetry of "Ought"

Here’s one I simply do not understand:

It is posted at an public access point at a beach in Surfside Beach, SC.

Isn’t the sign straightforwardly self-contradictory? Doesn’t “unguarded” imply the absence of a lifeguard? And if there’s no life guard, how can you swim near him or her?

Perhaps (likely!) there’s something I’m missing. But if I’m missing it, I’m guessing I’m not the only one.

There are, in fact, lifeguards along this beach, by the way. So “unguarded” likely doesn’t actually mean “without lifeguards.” So what on earth does it mean?