Here in PA red lights, red and white lights, red and blue lights all designate emergency vehicles. Blue lights, blue and white lights designate Fire, EMS, or K9 Search and Rescue personnel responding to a call. AKA blue and blue and white lights are courtesy lights only - they tell the general public that you are responding to a call. Sirens are only allowed on Emergency Vehicles. Now, if you're a Chief Officer (Chief, Deputy, Assistant, Battalion, FM, etc.) you can designate your POV as an Emergency Vehicle (Obtaining the proper forms and such of course) and have a red or red and white light as well as a siren. This is a choice, not a requirement. You can just run a blue light and no siren if you like.
I've come to realize that a majority of the general public is clueless when reacting to Emergency Vehicles.
Cases in point:
Several years ago I was riding Officer in our first out Engine, during rush hour of course. This Engine was BRIGHT yellow mind you, with an array of different warning features:
We were approaching a 4 way intersection, with a light. Our light was red. This was when traffic light preemption was just a dream. As we approached, checking traffic and preparing to make a right turn, there was a heavy cross traffic due to the time of day. Vehicular traffic on our left had stopped to allow us through the intersection. The lead vehicle on our right had also stopped to allow us through. Just before we entered the intersection, another vehicle to our right swerves around the stopped vehicle, into our lane, and back into his, nearly colliding with the vehicle in front of him, as well as us.
Responding to another call, same Engine as above, same road as well. Traffic was fairly light as this was a Sunday around 7pm in summer. I was riding Officer again as we were moving at a good clip - I'd estimate 60 MPH in this 45 MPH zoned, 2 lane road, with visibility at least 1/2 a mile+ (fairly straight roads with a few hills). Weather was dry. Anyway, most vehicles were yielding properly by hitting a turn signal or flashers and moving off the road (both oncoming and same direction traffic). We approach a Mercedes doing the speed limit. As he notices us, he speeds up and starts matching our speed approx 50 yards ahead of us. He will not yield. He does this for a good 2 miles, as I of course write down his license plate # on our dry erase board up front to provide to the Police.
These are just two situations out of hundreds, if not thousands, that I entered for a 10 year period while responding to both Fire and EMS calls. To this day, I STILL see people not yielding right of way to Emergency Vehicles. The biggest pet peeve I have is when an Emergency Vehicle is coming the other way, on a NON-divided road, you must pull over! In lots of cases that Emergency Vehicle needs both sides of the road to safely pass vehicles who have not moved out of the way enough. A majority of people do not stop, do not pull over. If I am in my Jeep, I hit my flashers or turn signal and move over. Several times when I've done this I've had ignorant drivers PASS me and continue on while the Emergency Vehicle was nearly running them off the road since they didn't yield.
If you still want lights and or a siren, check out Galls and their forums, as well as eBay, Craigs List and your local Fire/EMS forums.