I was told 1958 by the seller. I did remove the shroud and recall seeing a series of numbers but replaced the shroud before writing them down.That siren may have some years on it...I have a B&M S8 from 1957 that has the same 2-bar finger guards. The fine folks at B&M restored mine and commented those guards were changed in the early 60s. Since B&M made it for Mars, I bet they have info on it. Have you removed the motor shroud to see if there are any tags Or numbers stamped on the motor?