Well, this isn't really a "warning" device with reguards to emergency but it still relates to outdoor and vehicular signaling.
Anyway, does one know how the songs on an ice cream truck are generated and played ? I've heard a lot of different tunes in my neighborhood while growing up myself. Some I can remember were "Pop goes the Wesel" and "Do your ears hang low" http://blogfiles.wfmu.org/LB/0510/Pink_ ... wesome.mp3 in the early days.
Currently, I hear some "chime" tune that I can't identify right now and just two or three summers ago, I heard a truck playing a song that sounds like a cross between "She'll be Comming Around the Mountain" and another song I heard at Jr. camp once that I can't remember the name of; along with a female voice saying "HELLO!" at the beginning of every cycle.
http://blogfiles.wfmu.org/LB/Hello.mp3
What ice cream truck songs are played in your area ?