One of the main mistakes made by the guy who stamped the handcuffs (and probably lots of other items) is the fact that the SS (both military and political organisations) had no handcuffs of their own, in fact they did not have any handcuffs at all! German state security- and police units, like the Geheime Staatspolizei (GeStaPo) Sicherheitspolizei (SiPo), Ordnungspolizei (OrPo) and prisonguards did have them of course.
I agree with Atame that original items with SS-runes do/did exist. Most items in use by the SS (and other organisations that directly did belong to the German Nazi Party) had so called RZM (Reichszeugmeisterei der NSDAP) markings on them, in combination with an M code.
For example: this award was made by manufacturer M1/101 (Gustav Brehmer, Markneukirchen). Regular army issues were stamped with so called WaA markings, like this army saddle.
Ok guys, more than enough history lessons for today, I guess