Small lights on locomotives.

While reading my Trains and Classic Trains magazines I notice little lights on some locomotives. Old Alcoa’s have three on each side of the cab and some EMD locos have one on each side of the short hood. What are these for? Pardon my ignorance. Newbie. Thanks.

On the Alco's they are class lights -
Green - First Section of a schedule train with an extra section following
White is an Extra Section

The third light and only light on EMDs are Red, for when a locomotive is on the rear of a train.

That raises an interesting question: with the prevalence of operation on signal indication and/or track warrants, how many railroads still observe such train-order-era practices? Yet apparently, new locomotives are still provided with the traditional class lights (although red marker lights are still needed).

Classification lights/flags pretty much left the rulebook when GCOR and NORAC were adopted.

You might find a few museum or tourist roads that still use them for demonstration purposes, but I doubt you'd see them on a commercial operation.

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I believe older EMD units could display green and white classification signals. I seem to recall seeing F-unts showing white lights usually, for extras, which almost all freights on most roads despite symbol schedule.

I do recall when waiting for school bus [about 1963] seeing a PRR on the E&P in Jamestown PA displaying green for following section and about ten minutes second train came through showing the usual white signals. I know they were probably both extras since there was no tt authority [MBS using Block Limits], but they may have done it to attract attention so no one [such as mofw] would get onto track until both trains cleared.

Did see plenty of use of those red lights on rear unit whether pushing or running light on F-units to SD units.

The EMD style classification lights had a white lens, but had a little lever on them. If the lever was straight down then white light would show. Moving the lever one way would put a green tinted device behind the front lens, but in front of the bulb. Moving the lever the other direction turned it red. It was similar to how searchlight signal works. In Canada both CN and CP ordered their EMD locomotives with separate lights like on the Alco Century series.