Just joined the forum for this specific thread. There's a red Nishiki frame sitting at my local bike shop, early style headtube badge, looks maybe early 70s. Here's what's got me confused, the frame has no serial number, just an M stamped in the bottom bracket. The bb shell is in original paint and hasn't been ground down. Headtube badge appears original with the correct rivets and matching patina marks on the frame. Anyone have any idea what I'm looking at?