Hey!!! Just found some marks on this gun I had not seen before.
On underside of bbls just behind the male piece that inserts into the forend is "JM" and just forward of that piece is "JO".

Also, just in front of where it reads Choke on the bbls there is some strange markings that may be greek or something. Nore symbols than letters that are very small. Plus, here are some new Pix.