what is this icon in AE for?

[rickyl60209922]

May I know the funciton of this icon in AE? Can't I remove it or edit it? Thank you. 

[Roland Kahlenberg · Accepted solution]

That's a Visual Indicator the layer is the Fill Layer for a Track Matte hierarchy/function and the layer directly above it is the Matte Layer. HOWEVER, your Layer Index column, the column with the # Label shows your timeline has hidden layers. Look for the Timeline Shy Icon (shaped a little like Darth Vader's head) and deselect it, to show all layers, ie no hidden layers. 
HTH

[rickyl60209922]

Roland Kahlenberg, problem solved. Thank for your prompt reply and great help