As far as the normal military system goes (in other games as well), units are gaining ranks from nothing (recruit), one chevron for private, two for corporal and 3 for sergeant. All of them enlisted ranks. All of them have chevrons (aside of the airforce, which has v's like in the game) Those things in the game are not chevrons, as chevrons are like ^ not like v. It's an important fact, since military insignia are made in a certain way, chevrons pointing up, meaning upper class. Those might just be arrows from an ability casted on them by the zerg or by the ghost himself... I don't know either, but I don't believe those are ranks.