Along the Interstate 15 just south of Temecula at the border of Riverside and San Diego County is the small community of Rainbow (not to be confused with another Rainbow in Placer County, CA).
I've passed by Rainbow many times traveling on the I-15 when I used to work in San Diego two years ago but decided to visit the area again last weekend. My current interest is Low Pressure Sodium (LPS) street lighting which was once extensively utilized in the area due to the close proximity of Palomar Observatory in San Diego County (the monochromatic yellow color is easily filtered out by astronomers ) so I was really on a hunt for LPS streetlights but then came across North County Fire Protection District Station #6; also known as Rainbow Volunteer Fire Department. A SD-10 is located next to the station at the corner of 5th Street and Rainbow Valley Blvd
From what I could find out, the department uses pagers to call volunteer firemen. The siren, on the other hand, is utilized to alert the surrounding community in case of wildfire. Rainbow, along with nearby Fallbrook were affected by the Rice Fire of 2007 which destroyed about 248 structures in the area.