Sigil of Battle is give 3 might when weapon swap whereas sigil of corruption is give condition damage per kill. Sigil of corruption will stack regardless the dagger is on main or off hand. If I am not wrong, I believe you are talking about Sigil of Bloodlust which stack Power per kill. You can swap from Corruption to Bloodlust once you get 25 stacks. The only thing is you lose the stacks when you are downed or leave the map.
Little Furry – Twin Terror of Crystal Desert
Guild KöMÉ – §Strength, Honour & Duty§