A two foot mark is seldom co-incidental with with any joinery, and if it is, it is merely coincidence.
It is typically found two feet – from something. Often top of plate, or interface of tying joint, but there is variation on the theme.
I'm more than curious, and wish to know what key point in a scribed connecting girt barn would have typically been chosen from which to describe the two foots...
An educated guess, but a guess all the same, tells me it is likely top of tie – But we're gonna have to happen upon a number of them, either being dismantled or being resided or somesuch, to have some real sense of what may have been typical.
A two foot is simply a benchmark, a known point established in a first layup (typically two feet from a member that cannot be placed in followup layups) to aid in placement (and insuring proper relationships in geometry) in layups to follow...
As such, they are always found on reference faces, and so, are almost always buried by sheathing or decking.
A level mark, and any struck lines were used to level individual pieces in their layup or progression of layups.
Both marks are part of the layout process, to temporarily represent, to sort of stand in the stead for plumb and level. Neither is used or at least referred to directly in the raising process, but both are the best part of how the frame ended up plumb and level when it was raised.
"We build too many walls and not enough bridges" - Isaac Newton
