You probably already know this, but it's an SA (Sturmabteilung) Standard Service Dagger, adapted in 1933, with blade motto "Alles for Deutschland" (Everything for Germany). Maker's mark appears to be one of the early ones from Carl Eickhorn. K217SC is correct--there are a lot of fakes out there and the link to Tom Johnson should be helpful.
LTC (Ret) John R. Angolia's book, "Daggers, Bayonets, and Fighting Knives of Hitler's Germany" would probably be a good source (if you can locate a copy).
Are you close to Kansas City? If so, Manion's Auctions may be able to provide some more info on your SA dagger.
Good luck.