Signs of the age

Nicholas has a new obsession: Street signs. Every time he sees one, he has to ask what it means. He's especially fascinated by the red circle and diagonal line motif, the ones that prohibit whatever symbol is inside the circle. Like No Parking, No Trucks, No Smoking.
Then, of course, he must quiz me on why no dogs or whatever are allowed. His mom even bought him a book about signs.
The park district signs are especially instructive because they have three prohibitions and one rule for pets. So every time Nicholas sees that one he says:

"This sign says no guns, no parking on the grass, no drinking beer. And if you only have a dog, you have to scoop its poop away."

Every single time.
Yesterday we were at the ice skating rink and he noticed the sign prohibiting ice skates on the concrete bleacher stairs. Of course, he wanted to know why. I said, because the skates will chip the concrete and ruin it.
So today, he sees a No Trucks sign and asks why. I said, because trucks will ruin that road if they drive on it.
In a moment of epiphany, he says,

"The trucks will chip up the road, just like the ice skates will chip up the stairs."

Smart guy.