I'm really diggin' that green one. I got a couple crits (though they are very small, and sorta a matter of artistic choice).
I think that the guy's facial expression is bored/depressed, and I don't think anybody who's tagging feels like that when they are doing so, instead, they are kinda nervous (gotta watch for them pigs

).
Also, the spray coming out of the can looks very...messy, like its going all over and all coming out at once...I'd make it more of a funnel.
Again, just minor discrepancies; It's a great piece otherwise. Good job!