I have at least an 80s(possibly older) frame that has horizontal dropouts, lugged steel with brazing and hooks for a frame pump. The previous owner repainted it somewhere along the way but chemical stripper took it down to a yellow original color but no decals or head decal. No serial that I could find either. The only identifier that I could find is a simple "B-M" embossed in the upper part of the head tube lug above where the head badge would be. Is this a custom build or something of a nature that would not inherently have a serial since there is no evidence of an erased serial?