That's an interesting example to use. I only use turn signals when there are other cars around that would need the indication. I don't view a turn signal as politeness, its a safety tool to let others know what I'm about to.

I do also find that only using a turn signal when others are around is a good reinforcement to always be aware of my surroundings. I feel like a jerk when I don't use one and realize there was someone in the area, just as I feel like a jerk when I realize I didn't turn off my brights for an approaching car at night. In both cases, feeling like a jerk reminds me to pay more attention while driving.