We're guessing more than we know Lloyd, but DO know that Smith sourced Belgian "rough forged tubes" by Bauduin Doyen, Heuse-Riga Fils, Henri Heuse-Riga, George Laloux & Ernest Heuse-Lemoine, and those letters are not unusual. The letters are often partially removed with barrel finishing. Both barrels probably had 'BD' and 'H', and we don't know for sure who 'H' was.
There are a bunch of presumed importers marks also
https://docs.google.com/document/d/17ixogftgITEblNUWtmFBv96ZvgjK6eFell8GsAWd-KI/edit

https://sites.google.com/a/damascusknowledge.com/www/home