Yeah, I do the same with pannier, and think it helps. The arm idea is really a trade off, ****** off response to a couple of stupid close passes versus happy 99 percent of the time to go with the flow of traffic. In some ways it might cause more problems than it cures, I actually enjoy riding and treat interaction with other traffic as I would normally when driving. Almost wonder if I would actually come across more as a 'silly' cyclist by having something like this, still debating. Perhaps a hand on the end of the arm with the second finger raised? And for added effect, Stanley knife blades for finger nails?
Never attribute to malice that which is adequately explained by stupidity