Mr. Rewrite bets the cop's will give ticket's to any taxi's that disregard these sign's.
Yeesh. Let the AP Stylebook guide you on this one: No plurals from apostrophes unless you're dealing with an abbreviation with two or more internal periods (e.g. Ph.D.'s, M.A.'s).
Note to self: Ship these folks a few stylebook's -- er, stylebooks.