If you have a multimeter you can just intentionally short one end of the coax and then use the meter to find the other end of the coax. Only one will show a short. Label both ends and you are done.
You can do this with a piece of alum. foil stuck between the center wire and the connecting collar or with metal clip that will hold the center wire against the housing.
You can even make one with a 9-volt battery connected to a piece of coax center wire and ground and then a buzzer (Radio Shack $3) connected to another piece of coax the same way. Add a couple of barrel connectors and you can check either a cable or a wall plate depending upon the setup.
One of these:
Battery wiringand one of these:
Buzzer
