Equipping Trait I (one) in Arms causes Signet of Might to activate in passive mode, even if not equipped in a utility slot. This is great for signet builds, as it allows all 6 passive buffs to be applied if the other 5 signets are equipped
Warrior Trait bug: Arms I - Deep Strike
I can confirm this, Deep Strikes does give you a free Signet of Might for no apparent reason. Also you can refund traits and the signet will remain until you switch maps.