Your sign will go into Recharge mode when the voltage dropped below 10.5 volts.  This is to ensure the battery does not go completely flat and get permanently damaged.

The sign will automatically display the message again when the voltage goes back up to 12.5 volts.

If the sign is placed in a shaded area or under cover, it will significantly affect the solar charging ability to recharge the batteries and keep them running properly.  If possible, please move the sign to an open area with plenty of sunlight.

You could also recharge the batteries using an external power source to get it up and running quickly.

If you need the sign to start displaying immediately, you can OVERRIDE the recharge mode from the "More Info" section. 

NOTE: Using the Override Recharge mode is NOT recommended as the battery is still not up to the ideal operation voltage level of 12.5 volts. Override is only possible if battery voltage is 10V or greater, use this at your own risk as it may irreparably damage the batteries and will void the battery warranty.