Gun Control Act of '68 banned import of short barreled handguns. So your gun was made post war, (West Germany) probably between '52 and '67 and imported to the U.S. (import marks not required then).
My 6 year old "Blue Book" values German .22 PPK in %98 at $625. If gun is alloy frame it's worth less. .22 is worth more than .32 or .380.
Suggest you inquire here:
http://www.carl-walther.de/englisch/forum.html