It may be just a conspiracy. If you have ever looked closely throughout the tower at the banners being flown. You might see that the logo is a shield divided into four sections. The Titan, Hunter, and Warlock with a 4th panel that's empty. Also by the vanguard masters, surrounding their "war table" are 3 large banners hanging from the ceiling on all four sides of the table.... With room for one more. If you say that there is no particular reason for this then I ask you one question. Why ruin symmetry? Why not make three equal boxes within the shield? Why leave the empty space? To keep their options open maybe?
On the floors infront of every staircase, vendor, or wall is a picture of this shield bearing the Character Classes.... If you look closely you may see the outline of what may be the symbol for the forth class. I've asked around for people to share what they see when looking behind the diagonal lines of the 4th square and some say they see what appears to be a scorpion or a pair of horns. Maybe suggesting a class that does Poison Damage?
Maybe... We'll have to wait and see. What are some of your thoughts on the randomness of this logo, comment below.