QR Code Stencil Maker via F.A.T.
If you have Processing installed, you can run a Processing sketch that can convert a QR Code into a stencil (via a PDF output).
Yep, it’s a QR code stencil generator. We present QR_STENCILER, a free, fully-automated utility which converts QR codes into vector-based stencil patterns suitable for laser-cutting. Additionally, we present QR_HOBO_CODES, a series of one hundred QR stencil designs which, covertly marked in urban spaces, may be used to warn people about danger or clue them into good situations. The QR_STENCILER and the QR_HOBO_CODES join the Adjustable Pie Chart Stencil in our suite of homebrew “infoviz graffiti” tools for locative and situated information display.
More here, including more detail and instructions, as well as QR Hobo signs generated with the program
NOTE - the site says it has only been tested on Mac, though I just tried it on my PC and it seems to work as well :)