There is a bunch of different brownie graveyards floating around on the internet, but here is my version. Alright, when I say "my version" it really means this is how I came up with it given the random food floating around my house.
I made brownies...duh, and the graves are ginger snaps that I cut off the side. I used a steak knife and it worked well. I thought a small serrated edge would do the job just right. Then I took some chocolate chips and melted them down and used that for the writing. The trick here is to add a little bit of oil to it so it is smooth and won't get stuck in your piping bag (or ziplock with a pin-hole punch at the bottom). To get the dirt effect, honestly I had this on hand. I think I made it awhile ago by putting some chocolate chunks in the food processor for a few seconds. That helps give it that rough look.