The Banner of Rage contains the bound souls of the most bloodthirsty of Khorne's servants. It radiates palpable waves of anger and lust for slaughter which beat upon the minds of those near it, driving them into a killing frenzy. The banner may be used once per battle, in any assault phase (including your opponent's). Any models from the Chaos army (apart from those bearing the Mark of Slaanesh) that are within 2D6" of the standard, may add +1 to their Strength characteristic.
Banner of Rage
Source: Codex: Chaos Space Marines (1999), p. 28