The Message of the Day (MotD) is a section in the Alliance User Interface (UI) that can only be edited by the Leader of the Alliance.
Not Secure
The Message of the Day is NOT a secure form of communication. People outside of your Alliance can see what is written in an Message of the Day for an Alliance that they don't belong to. Disruptor Beam are aware of this issue but a fix has not been included in a Build Update as of yet.