I've seen skull and crossbones on gravestones in different parts of Scotland too. can't think exactly where, but I think I'm right in saying there's some at Dull (Nick Brand'll be able to say aye or nae to that if he's around) which would lend weight to the Templar and Masonic arguments.

also found this (minus the crossbones) at St Serf's Church in Dunning:

http://www.andysweet.co.uk/stones/skull.jpg

Cheers
Andy S