Unlike inputs 1-16, ST1 and ST2 do not show their assigned Name or symbol that indicates that their source is USB. I think they should.
In the image, compare:
Channel 12 (shows its assigned name “Click” and the “SD HC”-icon) with
Channel ST1 (does not show its assigned name “Gits” and no icon even though source is USB).
Even though the space is more limited, if the signal indicator LED moved over to the right, the name would fit under the jacks. The black holes in the jacks themselves would be replaced by the icon, twice.