by steven1981 on Fri May 31, 2013 4:35 pm
I suspected it was that source, since I saw ventilation strips on one side the actual housing itself. I notice that some housings that used neon as an illumination source had them.
Also, I am not sure if this might be significant, but if you look at "ALT," you could make out perfectly straight lines that are behind the letters (and perhaps the actual lens as well), which I think those are the neon tubes that illuminate the signal indication. I notice that characteristic in the old bulky Winko-Matic neon pedestrian signals, and I am sure it could be viewed in others that use lenses as well.
Steven G.