my first thought (and this is the first time i'm seeing this card), is that it's a "B" from a Boston (either Amer. or Nat'l team) player that was printed over the Marquard. i did a quick search on T206resource and didn't find an exact match, although there are a few cases where the "B" in Boston could be in a similar position...interesting & cool card.
http://www.t206resource.com/Team%20B...Checklist.html