It is a Weimar Germany era Police unit mark. S.D.IV.1449 means Schuzpolizei Dusseldorf, 4. Dienststandort (specific district of Police service) and 1449 is a police inventory number.
One of it's mates was recently discussed here:
http://luger.gunboards.com/showthrea...hlight=boehler
Cheers!!
Marc
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Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.