Brandon's Luger Configuration is right as rain for a 1937 no suffix. That is, all salt blue (including small parts) and the acceptance/proof marks. The Mauser Hump was incorporated as part of the normal production about the same time the change in finish was accomplished. The proof mark was changed to the eagle-over-swastika toward the end of the 1939 S/42 production.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />