In War & Conquest formed up units can become disordered; perhaps as a result of being charged in the flank and failing a command test, or crossing difficult terrain for example. You could make a note on your roster or put a piece of paper next to the unit but I prefer to have themed markers for this sort of thing.
So here are a couple of pics of my disordered markers for my Romans. Made from leftover bits from the Warlord Early Imperial Roman sprues.
and (without flash)
They'll also be handy for shaken markers if I ever get around to playing HC. I'll be making some more for the Auxillia, plus a few for my Celts.