Weird sign of the day – what does this mean?

Today’s weird sign is displayed after the jump (click read more to see it). It may be slightly “NSFW” (not suitable for work), but if you are at home, or simply don’t care, then feel free to take a look and post in the comments what you think this sign is trying to tell people not to do.

Yes, I know it is obvious what the sign displays, but I’m more curious why it is telling people that it isn’t a good thing to do this.

Perhaps it is just a weird and perverted way of telling people not to “honk” their car horn?