Hmmm.... maybe "I am not an illegal gun" since those are the ones people want to get "off the streets".
Other possibilities...
"sssshhh - you didn't see me"
"Advertise here!"
"If you can read this, you are too close"
"Keep finger off trigger until you have made decision to fire"
"Remove before showering"
"Emergency Use Only"
"Zombie repellent"
"Use sparingly"
"My kid is an honor student"
"Si Hoc Legere Scis Nimium Eruditionis Habes"
"Have a nice day"