I suppose it is possible that the owner did have the design proofread first, and the proofreader missed it. Either way, correctly using an apostrophe to form a possessive is introduced in second grade, revisited in third grade, and then should be mastered. Third grade!
Here's a few more from around town:
The problem isn't with "Jose's." That is correct - Smokey Jose owns the place, so it should be possessive. But, what does the taco own? It should just be "tacos" plural (as in more than one taco,) instead of "taco's" possessive (as in the taco owns something,) or "taco's" contraction (as in "My taco's too hot!") That last one would be considered slang, but it would be OK in quoted dialogue.
This one's not too bad:
When I find signs like these around town, I usually take pictures so I can show my students at school. We play "Spot the Mistake" since they are fifth and sixth graders and should be able to find them.
How about you? Do you have a pet peeve? (I hope it isn't people who silently correct the grammar of others!)