Too long and takes too much tme to think about it. But thumbs up for thinking about how to get the message across.
It's from someone else (can't remember who) but I like "GUN OWNERSHIP IS NOT A CRIME". That and the old stand-bys "When Guns Are Outlawed Only Outlaws Will Have Guns" and "How Long Does It Take A Cop To Arrive After You Dial 9-1-1?"
Whatever you come up with needs to fit in a box 11 inches long x 5 inches high when printed in letters 1 inch high. That's not a lot of space to get a message across that someone can read in less than 2 seconds.