Cordelia reads the note. Then she reads it again, thoughtfully.

"If you want to go with 'Captain Illyan' for simplicity's sake, you can. Signing 'Simon' is... Simon's way of subtly acknowledging that you're part of this family. You may address him as Simon now, if you choose. 'Captain Illyan' is neutral; 'Simon' implies... let's say, an openness to friendship."