A delightful message from a swing bridge across a river in the west country.
"When red man shows wait HERE"
It's a natural development of the illuminated road crossing sign found at pelican crossings, here adapted for river crossing. So typically it's illuminated signs depicting a stationary red pedestrian for stop, or one depicting a walking green pedestrian for go or walk. [Although it could be argued that it's not definitively a male, and could well be moon dancing rather than walking].
Really it's about the "light" depicting a red man coming on. The call to action is actually about stopping which can itself lead to waiting. Although one may choose not to wait of course and go somewhere else. So the message might equally be more explicit, something around....when red light shows stop here.
So the reality it's about stopping here, rather than the more appealing idea that could be of man dressed in red showing himself at that location and in an authoritative manner.