The M over the pick and "sole"( not really a sole, but a trough/sled/barrow for removing mined materials), is the mark for provisional black powder proof for shotgun barrels and rifle barrels for multi barrel guns( used 1945-1950). The 47S could be the model number. Black powder proof might indicate the gun was made for export to Russia. Jani is correct about the meaning of SP and Raimey is correct about Jani.
Mike