Enjoy watching my x-carve cut this sign into HDPE.
This sign uses 1/4" HDPE, black surface with white core. Mount it well. I use double-sided carpet tape.
There are two ways to carve this. The Easel file (linked above) will carve the sign with a simple pocket using a 1/32" end mill. This will take quite a while because of the small bit. You could adjust it to do a roughing and final pass carve as well.
The other option is the use the g-code file attached above. That g-code is set up to use a 60 degree v-bit to v-carve this sign. Created in Vcarve Desktop. It expects 8×12 HDPE, 1/4" thick, with the bit set against the top of the material in the lower left corner, as usual. It carves in a single pass.
Using an air compressor while carving can help keep the chips from melting into the freshly carved grooves. To be honest, I think I ran this too slow. You should carve at a fast feed rate, with slow spindle speed to minimize melting. I had plenty of cleanup to do.
I used tweezers to pick out the bits of plastic that were still hanging on after carving. Took me a while to get it clean to my satisfaction. Undoubtedly, running it at a faster feed-rate would have helped here, but it could just be that HDPE will always need a bit of clean-up. The V-Carved letters and image make it look great, but it will also be pretty good with a simple pocket mill.