I figured that was their basic way to call out the mike? (and the choice routes are those routes where they have options as to what they can run based on the coverage? like the curl/post/out route)
From my understanding (and I could be wrong)...
On running plays the mike is called out for someone to block (depending on the play, such as if the FB or C assignment is to block the mike), or for specific RB instructions (run at/away from the mike.)
On passing plays it depends on the play of course, but the mike can be called for either the line adjustments (if the Mike is to the left the LG/C double the DT on the left and pick up the mike if he blitzes) or in some plays is called for the RB to let him know who to block if he blitzes, otherwise he can go out for a pass, which is what i interpreted the C icon to be on those plays.
Pretty basic overall if true because it only uses it on specific passing plays (and I haven't looked closely at the plays that use it so I don't know if there is any specific reason for it other than...lets give the RB a mike assignment on this play because it would be cool.)
If I am wrong, is identifying in the O-line audible menu? Otherwise I don't know what else it would be or how to use it.