I had the idea of this dagger-thing a while ago. The idea is: Some hold daggers upside down and some hold them the normal way. With this thing you have both in one.
It's still work in progress. Would be cool if someone can model it in 3D (I tried and failed).
First drawn with pencil and then hand traced and coloured in inkscape.
See the double dagger at my deviantart gallery: http://panzi.deviantart.com/art/double-dagger-WIP-2-67343183