This is NY Mills NY's engine 112, maintained as a parade rig. NY Mills is a western suburb of Utica NY, a village with a fascinating history should anyone be interested.
All I can think of is that if this truck were leading a parade, they might want a light source that would be familiar and get the attention of the crowd. An old rotating beacon or wig-wag Mars light or Roto Ray (such as this truck might have sported in its heyday) might not grab people as much.
I guess the siren was on the left side -- we can't see it in the photo. I certainly hope that haven't replaced the mechanical one with an electronic gizmo in that light bar!
Well, they put them in various places on the open-cab trucks.
A rotating beacon might be on a short post attached to the top center of the windshield, though the windshield frame looks a bit thin on this one. It could also be on a tall post behind the cab.
Ditto a Roto Ray (see picture 6990). The Rotterdam Ahrens-Fox rigs originally had Roto-Rays, but they were swapped for other things later on. Maybe they were too strange-looking for European eyes?
A wig-wag Mars light might be over the windshield (see picture 5249) or on the nose above the radiator grille. I couldn't find an example of that on this site. I think 5249 might be the only Mars light on the site here.
I recall seeing nose-mounted Mars lights on Philadelphia, New York, and DC rigs; thy were quite popular in the in the 30s-40s-50s.
For European readers, the Mars light "wags" from left to right to left continuously. Later ones move the sealed-beam lamp inside its casing in a figure-8 pattern. Many current rigs still have these, in white or red. Have a look at picture 11082, which has Mars lights in both colors. That's a parade rig now, but the active suburban rigs in the DC area often have amazing collections of warning lights. In my experience living and driving there, DC-area drivers seem to be extraordinarily inattentive to their surroundings.
Interestingly, many US railroad locos also had white figure-8 Mars lights in addition to the steady headlights. This was before we starting requiring European-style ditch lights (pair of low-mounted headlights). Current locos often flash the ditch lights in alternation, when approaching a station or road crossing. Anything to get drivers' attention.
Yep, I think you're right. It looks like a combination of a siren with a flashing red light on the front.
The Philadelphia rigs I knew as a kid in the 50s had a "siren-lite", which contained a red sealed-beam lamp that would spin, generally mounted on the left front fender. I don't think the siren on this WLF is the spinning-light kind.
And on the roof or above the windshield, typically a Mars or Roto Ray. For some decades now the Philly rigs have used a red light bar and a normal LOUD Federal Q siren, which is REALLY popular these days.
Added by Mike Feldman on 13 December 2010.