Over the last few decades, more and more people have been casually using quotation marks. Quotes were once used when repeating what someone specifically said, word for word.
Now, quotes have a more sarcastic tone with the advent of the "finger quotes." With this new addition comes confusion. People don't really know when to use quotes anymore, and it can lead to a lot of awkward sentences. This is especially true when quotes are used for signs in public spaces.
I certainly hope the people who need to read these signs get "the message." Otherwise, we've been having a lot of people "serving" us food that haven't "washed" their hands.