But first... I guess I do have a few things to say about hand signals.
- Movement is more visible than a static pose. When starting hand signals, I tend to use exaggerated arm movements, sort of a "throwing" motion, to make myself more visible.
- The form of your signal can convey additional meaning. When merging into a left lane, I generally point at the ground with my finger, to say "I'm going there." Seeing someone point naturally draws your eye towards where they're pointing. My hope is that pointing where I'm going to go will cause drivers to look where I'm going, and thus be more likely to see me. On the other hand, when I am slowing down to turn left, I strech my left arm out with my open palm facing back, to say "slow down" to drivers behind me.
I don't use a mirror, but in normal traffic I can usually hear cars approaching from behind. When I'm being followed by someone who could pass me safely, but who isn't passing me, usually they decide it's safe to pass if I turn around and glance backwards at them. Turning my head tells them that I know they're there. Usually I move into the middle of a lane if it's not safe to pass me, but a quick glance backwards is often enough to encourage hesitant drivers to pass if I want them to.
Recently I discovered another technique, but it's a bit trickier to use effectively. In this case, the problem is that when I am stopped at an intersection and traffic crossing my path has the right of way, sometimes drivers stop and wave me across the intersection. Although they mean well, this is dangerous and they should not do it. It's unsafe for them to stop when other drivers expect them to be moving, and it is unsafe for me to move into the intersection when there may be other drivers who expect me to be stopped.
If you stare expectantly at drivers while waiting to cross traffic, they are more likely to stop for you, thinking you're a pedestrian. The key to managing this situation safely is to make sure they don't perceive you as expecting them to stop for you to cross. First, you have to make it obvious that you're stopped, and won't be moving into traffic without looking. Put your foot down, maybe even let go of the handlebars. Then, make it obvious you aren't paying attention to them. A glance at oncoming traffic when it's farther away may tell them that you see them, but then turn your head away and make it obvious you're paying attention to something else. Tell them that by stopping, they will only waste their time.
Unfortunately, I recently had another occasion to manage a driver's perception of my attention. In this case, a big white SUV was behind me on a slow, narrow side street, as I rode in the middle of the lane to prevent unsafe passing. I choose this route because it's slower than the main street, but occasionally cars use it as a short cut. She gunned her motor, intending to pass me unsafely on the left. By turning around and staring at her, letting her know I was watching her do this, I convinced her to stop.
That may seem dangerous, but I don't believe it was. Although it's not illegal to insult people, and might not be illegal to threaten them with physical harm, it is still definitely illegal to run someone over; even a self-righteous cyclist riding in the lane they're legally entitled to ride in (see also: self righteous, self-referential).
The greatest dangers a cyclist must contend with are not being seen by drivers, and not seeing dangerous situations they may ride into. It's important to use signals to tell other drivers what you're doing, but it's also important to learn drivers' signals.
For example, when a driver honks their horn at you, it means "I see you, so I won't hit you." If they gun their motor, they might pass you, so don't pull out in front of them; but it is also an indication that they see you, and will make an effort not to hit you. If someone yells "Get off the road" or something else (generally unintelligible) as they pass you, it means they see you. They may try to scare you, but they most likely won't hit you.
These drivers may be annoying, but they aren't the drivers you need to worry about, so try not to let them bother you. Of greater concern are the drivers who don't see you or who drive unsafely and unpredictably.