Most LED signs are connected via Engenius or Ubiquiti antennas. There should be one antenna in or on the building and one or two antennas at the signs. You can check the connectivity status by looking at the lights on the antenna.
If you have determined that your antennas are from Ubiquiti, you will need to run the ubiquity discovery tool. Click HERE to download the tool. After downloading this zip file and extracting it, please run “ubnt-discovery-v2.5.1”. If it has a popup asking how to open this file it means your computer does not have Java installed. If this is the case, run JavaSetup8u231 to install java and then try running the discovery tool. When you run the tool you should see 0, 1, 2 or 3 antennas. If you do not see any antennas it means there is a communication issue between the main computer and the antenna. If you see 1 antenna it means the antenna is not talking to the outside antennas. If you see 2 then most likely everything is OK unless you are supposed to have 3 antennas.