Martial Arts training might be a candidate, not the choice of doing it, but where and when to punch / kick exactly. You signal via success of your strategy, but I think you do not signal about which way you achieved your success. This might obviously be different for different styles of MA, I only have experience with Ju-Jutzu. Also, I think this example might be interesting, because the mental effort is high compared to some of the other examples.

Regarding Nose-picking, I think it is a quite signal-high activities if done in public. I'm not sure what Nose-picking signals though, but since nearly all parents constantly tell their children not to do it in public, the probability of it having signaling effects is extremely high. So at the very least, not doing it signals "I have a good upbringing".