Each signage device attempts to communicate across the network to the SignStix server on a regular basis (at least once per minute).  This allows the device to tell the server about its current state (e.g. its temperature, how long it has been running) and ask whether new signage is available. 

If a networking issue causes this communication to fail, the device will continue displaying its current signage, but it will not be able to download any new content or upload information to the server until the network is restored. 

Please see the following link for troubleshooting your offline device: https://www.signstix.com/support/troubleshooting/my-signage-device-has-a-red-dot-next-to-it-in-director/