BruceS:I don't know how common they are. I haven't seen any headstones with death masks, I have seen a few sarcophagi with death masks.
Yeah, I've never seen any of these, either, and I've looked at a lot of headstones! I haven't been everywhere yet (BruceS has, I think - except Hawaii) but I think there may be a serious lack of prevalence propblem with this one.