I've seen a technique used to mark properly torque fasteners, which is to torque the fastener and then use a sharpie to draw a line from the center of the fastener off to one side of the surrounding material.
I've heard that a clueful inspector will understand this, and recognize it as meaning that the electrician actually took the time to properly torque the fastener. Of course it doesn't actually say what torque values was used, and nothing prevents someone from simply marking any random fastener.
I like the approach of recording the torque value that dmattox suggests. This permits an inspector to double check which torque value was actually used, and is a pretty nifty workmanship detail.
-Jon
