I know that there is an X Marks The Scot tartan, an X Marks The Scot plant badge, an X Marks The Scot crest (gotta get me one of those pins…)

But…

Is there an X Marks The Scot motto?

If there isn't, I suggest:

Semper Fidelis Subligaculumi.

This is Latin for "Always Faithful to the Kilts." If I messed up with the grammar at all, mea maxima culpa.