Doesn't everyone carry a ladder while trekking? Surely essential when climbing a tree to escape bears. But any metal short circuit across the rails will do to put signals at danger, whether in the wilderness, in town or elsewhere.

Out in the wilderness signals will be very far apart. Chances are there isn't going to be one between you and the train.

Netstruggler: True, but better to take the chance of stopping it than to guarantee to wreck the train. In any case, I seem to remember that the incident that sparked this thread was in a busy city environment, (which was rather the point of it, in fact)

Police cars usually have jumper cables available to help someone with a discharged automobile battery. If anyone had taken a jumper cable and connected it to both rails before unrolling the yellow tape around the scene,, it likely would have informed the train signalling system that the track was busy, causing a stop signal (in the cab or along the wayside) to approaching trains. It also would have caused a nearby crossing gate/signal to activate.
Signaling systems detect trains on the tracks by measuring resistance between the rails on a given section (block). A train's axle (or your jumper cable) will trigger low resistance, which is detected as the block is busy.
Another approach would have been to call the railroad emergency number. The police officers' dispatch should have been able to do this as there was a bunch of time after landing.
With all that said, this is incredible bravery by the officers on the scene and a fabulous rescue of the injured pilot.

NTSB does both; all types of transport.