On the OP's revolver: W.B. are initials of Colonel Waldemar S. Broberg, who was Ordnance Inspector for the Army during the period when these revolvers were being made. Late in the War he served in the South Pacific and was decorated.
A little info:
Col Waldemar Sven “Gus” Broberg (1896-1970) - Find A Grave Memorial
Most of the BSRs found in the US are covered with miscellaneous proof, service and origin marks that were hammered into the steel when the guns were released to commercial enterprises by the British military after WWII. This one is to be prized not only for its excellent condition, but for its freedom from those unsightly non-factory marks.