Double Double Errors

[kimbalaya]

Some time ago, I took a photo of a sign standing near the sidewalk next to a local Mexican restaurant.  I hadn't gotten around to posting about it yet, but now I have to.  Note that this sign has two errors.



The reason I have to post this now?  Yesterday I was driving past this restaurant and discovered a new sign, advertising more specials.  This new sign also has double errors!



What on earth is o/z ?