He's been rapidly allowing touch from others; not just Istredd, but casual acquaintances, too. She is the source of that progress.

He doesn't know the sigil, and maybe that's for the best. He won't know it might be what keeps him from going all the way and killing Kyle, Kell be damned. He won't know it might be what stops him from continuing to ruin his relation with Jack before it even started, or if that would really be simply the reminder of her in general.

He does know that she wouldn't do him harm with whatever this was.

"No promises," he tells her before grinning. "Your friend Natasha is a fascinating individual, by the way."