Signs at San Onofre Beach

After coming in from a morning surf session in San Clemente, I took some quick shots of a few signs that caught my eye. "Surfer Mom" and "No Pop Outs" are easily understood by anyone who surfs. I'm not sure though what "Do Not Hump" means with regards to that train car. Camera: Pentax K100D; Lens: FA 50mm f/1.4.