How do you distinguish a composition representing footage from a composition you are using for compositing? Composite has a role for a composition named Footage.

A composition with a Footage role displays a different icon in the Tool UI.

This role is not permanent and can be changed at any time. You can even create a composition from scratch and assign it a Footage role. When a sequence is imported, either by clicking the Import button or by dragging the sequence into a library folder, a composition is created with the Footage role. The role of a composition does not change its behavior at all in the application, and is only used as an indicator of the intended use of the object.