When you say you want the model hash for the sirens, do you mean the lightbar on top of the police car? If so, I think ch3y3zze is correct in that the lightbar is a component of the main model, so I'm not sure you are going to be able to spawn the lightbar by itself.... Is this what you're meaning? Perhaps we could help you if we knew what you were trying to do, but if we've answered you're question, then that's cool!
Hope I've helped!!!