I thought two syllable "hashtag" was verbally chunky when "pound" works. But three? I guess I started out calling it the "tic-tac-toe" sign as a child.
Actually, it took a few phone calls to Luxfer and then Metal Impact (Thunderbird). Nobody knew. Then someone at MI remembered somebody working there that had been there for ages and asked them.
Once upon a time, if they had bottles that came out of the extrusion and crowning that had discolored (darker grey or streaked) appearance they would acid wash the bottle and mark it with an "#". Even old, these bottles seem to have shiney bellies inside.