Funny this topic came up, as I was discussing this with my pipe instructor this evening.
He commented on my tattoo on my calf (A celtic cross), and said that a buddy of his, in the black watch, had a tat of a sgian dubh on the outside of his calf. Apparently, a few years back the black watch took all the sgian dubhs from the pipers (he didnt say why). So, they all went out & got tats of either a sgian dubh, or one of the thistle.
Didnt mean to hijack, just thought it a neat story.