http://www.gingerb.com/CNJ%20Mauch%20Ch ... 0Train.jpg
There's a pic from 1944, with the statue herald on the tender of the engine, but no orange disc on the cupola of that 2 year old steel hack yet.
http://www.gingerb.com/CNJ%20Mauch%20Ch ... ew%202.jpg
Nearly the same spot, 17 years later.. It's 1961 and two out of the three hacks pictured have the orange discs. I'd venture to guess the started putting them on in the late 50's.