There are the Signs That Make Skateboarding Look Cool. I like these the most, as the coolness of the images cancels out the skater-hater message of the signs.
There are the Signs that Make Skateboarding Look Totally Uncool
There are The Signs That Are All Text, Very Serious, and Sometimes Legally Fallacious
And then there are the signs that have been modified to say something new:
Another weird group of signs ban the board (metonymically) as a symbol of the larger activity: