Guild Wars 2

Sigil of Perception (+10 Precision per kill) does indeed stack with Sigil of Accuracy. However, Sigil of Accuracy reports +5% crit chance, yet only delivers +3%. I am assuming this is a bug and have used /bug to report it as so.

Sigil of Perception will NOT stack with Sigil of Bloodlust, Sigil of Life or Sigil of Corruption.
None of the 25 kill sigils stack with each-other; your 25 kills will only ever count towards one of the sigils. Otherwise, it would be very possible to build up +250 Power, Precision, Condition Damage and Healing Power.

I hope that helps.

Edit: To clarify, my warrior’s melee weapon set is an axe of rage and a warhorn of accuracy, with a rifle of perception in the alternative slot; I have checked, and get the benefits from both sigils. Benefits are visible by checking crit chance in your Hero window. I build up the Sigil of Perception by getting kills with the rifle, which then contributes to my overall Precision rating until I’m downed. Swapping weapons does not kill the stack, unless the newly equipped weapon has a different “Per Kill” bonus.

It’s explained in the wiki : http://wiki.guildwars2.com/wiki/Sigil#Stacking_and_charging