I had the same question a few years ago, so I emailed the PGC.

I don't have the letter any more, but I do know that it is legal to use them to hunt deer from. I remember them saying that you can only hunt turkeys from blinds made from man-made materials that cover you completely, but for deer, they said anything goes. You can hunt from natural blinds (ie: logs, rocks, stumps, dirt piles, brush), or man-made blinds and it could or could not conceal you completely. I do not however remember if they said you needed to put orange on the outside of the blind if it concealed you completely. My brain is telling me that you didn't need to, but I'm not sure.

Hope this helps...