The Devices page in Director lists all the signage devices known to the system. In the info column for each device is a 'traffic-light' dot, showing its current network status:
Red- The signage device has not been able to contact the server for over 20 minutes
Amber- The signage deice has not been able to contact the server for over 3 minutes (but less than 30)
Green- The signage device has successfully contacted the server recently (within the last few minutes)
If the colour is amber or red, there may be a network issue preventing communication from the device to the SignStix server.