When you take Signet of Agony, it does not seem to apply the slow from Crippling Anguish, nor the Death Mark from Frailty. Unsure if this is intended or not, although if it’s fixed, it would also make the player character perma-slowed/marked, assumedly, so that should be considered when adjusting it, as that would be quite a hefty investment to make for what Signet offers [outside of the rip blood interaction when maxing Swift Release].
Additionally, there is a very odd interaction between Signet and Bone Prison, wherein if you take both, the Bone Prison still spawns, but only after the aura gets turned off [usually from the player running out of mana]. With this in mind, I tested to see if something similar happened with the slow and death mark, but that is not the case, it only has this funky occurrence with Bone Prison.