[Those rings don't let them bring others with them, which was a shame. Maybe they should drop a rumor to the Cult of the Fox that Tarz was in possession of a sigil. Saber knows what happened to Lancelot. Let Severine kill Tarz for them.]

Your luck would probably have Tarz insulting your honor if you spoke with him anyways. [Which would give him a just cause to challenge him...]

Perhaps conversing with Lancelot is the best option right now.