i dont know if this has already been mentioned, so im sorry if it has. in the Metallica song "Escape" on the Ride the Lightning album theres a siren in the middle of the song. it sounds like an old single tone siren from WWII or something.
what about the siren in the Black Sabbath song War pigs... I think these sirens are all taken from an already recorded source. The london archives or something?
Jailbreak - Thin Lizzy (recording of a single toned siren)
Ridin' The Storm Out - REO Speedwagon (synthesized wind-up, start and end)
Welcome To The Machine - Pink Floyd (synthesized dual tone, end)