Clean “BEACH’S”?

New signs attached to posts near the surfer’s beach / harbor area appeal to the public with: "PLEASE KEEP OUR BEACH’S CLEAN"

I really like the design and composition (bold yellow letters on brown), as well as the size and placement, but…

As a teacher, I wonder if the donor might be willing to correct the spelling/grammar on the signs. 

Otherwise we may be faced with rampant misinterpretation as a Coastsider’s Mad Lib: "PLEASE KEEP OUR BEACH’S _____(noun)_______ CLEAN".  Although that could work, too.  ...keep the SAND clean; keep the WATER clean, keep the AIR clean, etc.

The effort put into making and posting those signs is commendable :-)

Thanks.