Best Practices for Using Brass Standoffs Electrically?
It is quite common to connect to chassis trough these connectors, so why not a signal? I kinda like the idea. Integrety-wise it would be a bit shady when considering return currents, current loops and that kind of thing, but as long as you factor that in it could work.
Star washers has been mentioned; I would never ever use star-washers anywhere near a PCB. If used on a PCB it will just dig through the copper, so that will not at all be helpfull. Any star-washer will create a fine metal dust during vibration. Needless to say that can be lethal for a circuit even if the star-washer is on a mechanical assembly nearby. What you want is a copper-beryllium crinkle washers, and probably an ENIG surface-finish on the PCB.
I am not sure if brass is the most ideal standoff material, but how worried you need to be on oxidation depends on the enviorment.