Re: Walther PPK sn 182960K
The Crown/N dates the pistol to, or prior to, 1940, when the proof law was changed to make the proof mark the Nazi eagle. The N indicates Nitro (smokeless powder) proof.
It looks like one side laid in something wet at some time, and lost its bluing. You don't say, but it is probably .32 ACP (7.65mm). If it is .25 or .380, it is worth more.
Assuming it is .32, a nice blue on both sides would make it probably an $800 gun; as it is, maybe $400.
They are beautifully made guns, quite reliable and accurate.