I wanted to paint a punisher skull on my AR and I wanted to get a couple pictures first and ask around on how everyone else does it.

spike tacticle sells stripped lowers with the skull laser engraved for about $130 I think

Funny you should bring this up I just finished up a punisher logo on my Mossberg 500 (I know not an AR) with Krylon.  I just googled the punisher, went to google image, and selected large images.  The one I found had to be cropped a little with an editing program.  Then I just cut out the stencil and applied it to my stock with some blue painters tape.
   I'll see if I can post some pics later, I think the "teeth" on the skull didn't come out so well, I may invest in some stencil paper with a sticky back from now on. Jim

you can also use stencil spray that is like a low tac adhesive spray paint.  It works well with mesh cloth as well.  I typically just use water misted on to "stick" the paper to the part.  Blot out any water within the stencil area and then spray.  I do this when I am applying stuff to pre-cured parts and am too lazy to bake between colors.