I agree it is not a Mossberg mark, there are 4 I have examples of, none are like that. Also, mossberg seems to have used horizontal fraction lines.
The weird fraction thing is, Williams went out of their way to advertise that they *only* produced *drop forged* wrenches...
But who knows, they may have succumbed to the market at some point...
The only other possability I can think of is Wakefield, but I have never seen them use any mark but their name...