It indicates there is a problem with the WiFi connection being used by your PiScreen.

Usually, the problem is with your network router. 

• It could be offline or temporarily disconnected from the internet.
  • Check it is working by trying to use your wireless network from another device. If it isn’t working follow the guidance in your router manual or call for technical assistance from the person or department responsible.
  • If you found and fixed a problem with your router, you PiScreen will automatically recheck the network connection. If  successful, a message confirming connection appears and the corner symbols show no more.
• If your WiFi network password has changed; perhaps because you have changed your network provider:
  • Using your phone, tablet or laptop, search for a WiFi network called PiScreenConnect. The password is PiScreen.
  • Enter http://192.168.4.1 into your device browser address bar.
  • On the form presented you have two options.
    1. Press the button at the top of the screen to “Retry without changing my WiFi details”.
       Use this button if you have resolved an issue with your WiFi access point but have not changed the WiFi password. 
    2. Select your WiFi network name (SSID) and enter your new password.
       Press the connect button and wait.
  • If the password has been entered correctly, a message will appear on the screen to indicate successful re-connection and the symbol above will stop showing in the corners of your screen.
  • If the password was not entered correctly, reconnect your device to PiScreenConnect and return to http://192.168.4.1. Re-enter your password and try again.

Note that it can take a minute or so for each stage of the process to complete. Please be patient and watch for messages on your PiScreen.