Shimano gear indicator stuck
Remove those two screws visible in the picture and lift off the indicator. It may be that the mechanism to move the indicator has become dislodged. 

You could, as I do remove the indicator completely. Sometimes underneath there is a blanking plate you can use to cover the hole. You don't need to see which gear you are in and it means you can move the lever closer to your brakes for a tidier bar layout.