It's optional and everything, but contributes to the whole guild thing.

If you use a faction title (including "SeeD"), you could get creative to accomplish the same thing if you'd like. Otherwise don't worry about it, having a faction's title is also good for the guild.

This only applies to MSN, any format works in other places such as games. Using a tag there is also highly recommended, but it's entirely up to you how it's done.