The Solms-made M6's also say "Made In Germany".

But the Solms M6's say "Leica Camera" or "Leica Camera GMBH" on the back along with the "Made In Germany". I presume the Wetzler cameras would have "Leitz" instead of "Leica".

Serial number is on the accessory shoe for all.

The shoe does seem like a dumb place to put it, now that you mention it.