Before anyone mentions bells... Years ago, after several walkers suggested that I should get one, I did. I then discovered that about 1/3 of people like them, 1/3 are so deaf or distracted that they don't hear them, and 1/3 find them annoying. One person didn't react to the bell so I used it again. He then said that he was not going to jump every time some idiot on a bike rang a bell. Furthermore, if I rang it at him again he would tear it off my bike and stick it up where the sun doesn't shine!!!
I don't bother with bells now. If I have to, I just cough at a distance to alert the walker, or call out a polite request to let me through.