They are commercial proof marks, the Crown/N is the nitro proof, the StmG is for steel jacketed bullets. Not sure when the C/N changed to E/N, 1939-1940, but the siderail suggests this is Imperial or shortly after, DWM changed names shortly after the war and stopped making rifles quite early. They piddled with P08's but none of this is an interest of mine (commercial production).
In short I do not know much about this rifle, though often a date can be found on the barrel, typically under the stock, you should at least examine the barrel for further clues. Others can probably answer your questions better than I can, Gunboards-Mauser is a good place for this type of information, - here most people focus on military rifles, Gunboards-Mauser have a more diverse crowd.