If it's a Pace RNG110 box, that means there is a on screen message waiting from Comcast.
To clear your message, press "menu" "menu" "messages" and read and clear the messages.
You can also turn off the message indicator permanently by going into the "menu" "menu" "setup" "guide setup" Scroll down to page 2 to message indicator and turn it off.
That worked. Comcast wanted me to know the latest Hobbit movie is available. I went to the Guide Setup and turned off the light. I wonder if anyone at Comcast ever thinks about how their aggressive marketing comes across.