A trail marker matters most when the path stops looking obvious.

Signposting always looks redundant right up until it does not. On the clear stretch, a marker seems like clutter put there for people who cannot manage; at the point where three routes look identical, it is the only thing standing between you and an hour of walking back. That is why so much of it gets removed by people who have never been lost there.

Whatever you write for others, put the extra sign at the confusing junction, not the clear one. The caveat in the instructions, the note at the tricky step. It will look excessive to everyone who already knows the way.