As I was jogging down the bike path, a biker passed me going the other way. I noticed as he slowed to pass me, he made the universal hand signal of slowing down - arm crocked and hand down. He did this to alert those around him of is intention to adjust his trajectory. He put people in his direct environment on notice. Those who would potentially be affected by his change in behavior could now adjust their expectations accordingly. This is great! This is high frequency, low magnitude communication at it's best. Keep this visual in mind - simple, universal signals to communicate your intentions, so those who may be affected can adjust their expectations and actions accordingly, and avoid a messy "crash."