Normative Signs: The Poetry of "Ought"

This was taken at Peet’s Coffee, in Cotati, CA. Does the person who posted this sign have a sense of humour, perhaps? Or does he or she truly worry about patrons drinking from the toilet? Is this establishment frequented by dogs who can read?

(A further alternative, I suppose: is the posting of such a sign an overly literal application of a regulation of some sort stating that any reclaimed water needs to be “labeled”?)

The picture is by Rich Way, via Thea Smith.