I believe hes referring to the alternate marks of Power Armour, descriptions of such are found on 149 of Deathwatch: Rites of Battle. Things like the beakie Mk6 Corvus Armour or the knightly Mk3 Iron Armour. The Mk5 Heresy Armour is especially well suited to a traitor marine, while considering how shiny and new it is, the Mk 8 Errant is probably out unless he pilfered it off a Captain last week.