Ford Five Hundred Radio Indicators

Does anyone know what the little headphone symbol means on the Ford Five Hundred radio display?
I've never noticed it before and mine is now on. There is no description
that I can find in the manual.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.