If I recall Rule 99 correctly, there was something to effect that if the train was stopped "and likely to need protecting from a following train...." you needed to flag. Obviously early in the morning, southbound at Needleton, nothing is going to be behind you. But hopefully, the brakie was simply posing for the pic. the spout is not down in the tender, so they either just stopped or are about to leave.
Only a couple of times when I braked in DUR did I need to "really flag". One rainy day we were having lots of traction issues, nearly stalling in several places. We were getting to be 30+ minutes late and the next train was scheduled only 45 minutes behind us. Finally we spun to a stall near Needleton and the engine crew decided to perform some surgery on the sanders. I hightailed it about 1/4 mile. When called in I left fusees for the next train, who actually was close enough behind us to find them still burning.
Another time we were southbound at Cascade, running late and had to pick up the Railcamp car. Theoretically, the next train was only 10 minutes behind even though I knew they were running late too. But I did my thing and hoofed it back quite a ways. I almost didn't make it back to the train before they highballed out of there. This time, the following train was still quite a ways behind us, and never saw a burning fusee.