On a 1995 land rover discovery What is the dash board symbol that looks like a trailer mean?

It's a green light that should flash once every time you put your signal light on (either direction). This light tells you that the trailer wiring system that was built into the Disco is working properly.

When you tow a trailer and connect the trailer lights to the LR wiring connection next to the hitch, the green "trailer" light on the dash should flash in sync with the signal light arrows every time you put on your signal light. This is telling you that your trailer lights are working properly. If the green "trailer" dash light does not flash, then you might have something wrong with the trailer lights or with the wiring.

Unfortunatly Land Rover abandoned this feature on the Disco II.