An apostrophe too far

Whenever I come across some mailbox with something like “The Johnson’s” on it, I want to park my car, walk up to the front door and ask the occupant “The Johnson’s what?” Because the plural of the preponderance of English nouns is formed by adding an S; it never involves an apostrophe.

But I don’t, because I don’t carry a whiteboard around with me. Also, I don’t fancy getting into a fight over it.

And I know it’s pretty much a losing fight—the barbarians are winning this one, and it’s getting worse.

Viz. this sign found at a grocery store in California:

I hope it’s someone taking the piss, but I fear it is not.