A way for creepy people with porn mustaches to say hello or "I understand". Hold your fingers in the shape of guns (use both hands for maximum effect) and point at someone who just arrived. Bend thumbs to simulate shooting your finger guns and make a clicking sound with your mouth. May be accompanied with a wink in extreme cases.
That dude that looks like he just fell out of the 70's just offered me a piece of candy and then winked and gave me finger guns. I said no.