The Breakfast Club is well worth the wait, and I'd say that unnecessary apostrophe is really the only regrettable thing about this delicious breakfast option.
It just doesn't make any sense without the apostrophe. If you're going to bother to spend the money and get a vinyl sign printed, couldn't you at least proofread it?
This apostrophe is technically used correctly, if the store was owned by a guy named Sam Walmart. Unfortunately, his name was Sam Walton, and the name of his mart was Wal-Mart. Get it? Great. Stop making it possessive....or plural. Unless you are referring to a group of them.