This is the logo I use for the hardware I design in my electronics projects.
It is simple, and more suited for being included in board layouts as it only uses lines and arcs.
Here you can customize it, generate your own version, and save it for your favorite CAD tool (gEDA pcb, KiCAD, or eagle).
I hold no rights on this logo and you can do whatever you want with it.
But preferably use it for open source hardware projects (which ever definition and licence you are using).
unit: