Dinah's horn is not a locomotive horn, which would be a whistle in any case.
It is a dinner horn, similar to a boat horn, traditionally used by cooks to call workers in from distant fields. Loud and raucous, and when you hear it, you know dinner's on.

In answer to Chicken Charlie (wherever he may be after these seven years) I'm going to start a new thread on "Workin On the Levee."    It is a distinct song, though it seems to have gotten entangled with "I've Been Working on the Railroad" back in late minstrel days.

Bob