I think Bramah was writing in a time when the idea of ‘privy’ marks on milled coinage was widely accepted, as the 1897 ‘dot’ penny. I would consider the mark below the ‘T’ to have some other, non deliberate, origin unless it could be definitively proven otherwise , which is unlikely now. I don’t know of contemporary Victorian forgeries that would require differentiation from genuine by a privy mark, and die studies were openly undertaken by die numbering or lettering.
Jerry