Re: Question...

Well, you make this difficult by have the engine coupled the wrong way to the train.

Generally, the signal to an engine is based upon the normal position to the engineer's position. A back-up signal by the brakeman or conductor would be made if the Johnson Bar or reverse key, in an electric or diesel, needs to be in the reverse position for the engineer.

The engine would then signal three shorts to indicate a backing move.
------------
Multiple locomotives (double or triple headed) can make for some interesting whistle signals

The complicated part is that two-shorts is to indicate a forward movement and two-shorts is also often used to respond or to acknowledge any other signal. This is where different railroad's rules might differ.

Say you had a double-headed or triple-headed steam train. For the forward movement the the lead locomotive would receive a signal from the trainman, then blow two-shorts, then each of the following locomotives, blowing two-shorts in turn, after the last locomotive signals then the movement would start.

If for some reason the trainman signals for a back-up movement, the lead locomotive blows three-short and each additional locomotive blows two-short to acknowledge. I recall riding a triple-headed steam train on the Sierra back in the 1970s. At a run-by this was the procedure used. It makes you stop and recall the purposes of the various signals.

Brian Norden