New Plural Rule - A=Apostrophe O=No Apostrophe

This is the sign from an establishment on the Boardwalk in Ocean City, New Jersey. As you can see, plurals of words ending in O are formed properly while plurals of words ending in A are formed with an apostrophe. I suppose that's a new rule learned only in select elementary school English classes. S after O but not after A, instead you insert an apostrophe. It's taught right after the lesson on adding -es to make a plural and just before the lesson on deer and deer.

It continues to beg the question whether the sign makers say anything when presented with the instructions for the sign.