You need to enter something as a signature. Go into the User Control Panel (top right of this page above the Donate button), select Profile (left side) and Edit Signature (also left side) and type in your rank, name, unit and army e.g.
Lt. Arnold Ziffle
1st Hungarian Rifle Battalion
2nd Brigade
1st Division
Anglo-Allied Army
Something like that. You can personalize it any way you want really, but the French officers are going to want to know who is challenging them. You know, they need to know what to put on their tombstone in the "Killed By" section.
Thanks!