Has anyone else ever seen someone with a waffle-like imprint on their scalp?

I was on the metro today and stood above a man who had what appeared to be a waffle-like imprint, perfectly rectangular, on his scalp. He had a full head of hair except where this imprint was. The "waffle squares" were indented and were about 2x2 cm each. Has anyone else ever seen something like this? Could it be the result of surgery or some strange branding?