Guild Wars 2

Any definitive tests on Sigil of Smothering stacking with Sigil of Night?

I don’t know of any testing, the wiki seems to think that flat bonuses don’t stack.
If you want to test it yourself make a Warrior go to The Mists, equip steady weapons, try Sigil of Force and the Sigil of +damage to CC’d targets, then use Bull Rush against a golem and compare against steady weapons with just one of those active