Theres a double headed lion as a stone masons mark in ST GILES CHURCH, CRIPPLEGATE City of London. Probably nothing to do with it but here's a link.
http://www.middlesex-heraldry.org.uk...ripplegate.htm or wade through this lot.
http://www7b.biglobe.ne.jp/~bprince/.../fdguide11.htm though this seems to be nearer the mark......
FIG. 290.--Lion rampant, tail elevated and turned over its head.
FIG. 291.--Lion rampant, with two heads. FIG. 292.--Tricorporate lion.
Lion rampant with two heads.--This occurs (Fig. 291) in the coat of arms, probably founded on an earlier instance, granted in 1739 to Mason of Greenwich, the arms being: "Per fess ermine and azure, a lion rampant with two heads counterchanged." This curious charge had been adopted by
Mason's College in Birmingham, and on the foundation of
Birmingham University it was incorporated in its arms.