"Wet Paint" is a phrase used on signage, commonly seen on Sesame Street. It is a warning to the reader that a nearby object has recently been painted and that caution should be exercised within its vicinity until such a time as the paint has dried.
Several pieces of media have been titled with the phrase:
The concept has been communicated many times in songs, books, and sketches not only as a cautionary warning, but also to the detriment to characters and amusement of bystanders (and the audience):