T-Pein could give his sword to anyone. That person will be informed that they have received Oathskeeper. That sword belongs to Jaime, so they know Jaime is in the game.
Sam has the sword Heartsbane. In the show, he gives it to Jorah in the fight against the Night King. The sword existing *should* mean the Night King is around. Ergo, if I give the sword to someone, and ask them to claim that they received it, it means I gave them Heartsbane. No Lannister, nor the Night King, nor Littlefinger, nor Victarion, even possesses Heartsbane. Q.E.D, by me giving them Heartsbane, it means I am who I say I am.