The question is, humping what? Those pillows have a lot of yield.
The Redditor who took this pic spotted it next door to the room where he and his family were staying, in a hotel at Walt Disney World (the Hilton in Buena Vista Plaza). We admire the occupant for not mincing words, but if he or she is going for accuracy, the sign will have to be edited several times more to keep up with the stages of coitus. Humping will have to be crossed out to read, "Basking in the afterglow," or, more likely, "Apologizing." Then comes, "Rinsing Up." Then, "Trying to figure out how to ask him/her to leave so I can get some sleep." Maybe it's better to keep it vague.