Would you bother preparing something to help prove your reincarnation, or would you simply take advantage of whatever you retained (and prepared for yourself) from your past life?
How might you use this ability to help yourself and others?
Edit:
To clarify, suppose you have some vague memory of your past life in your reincarnated self that helps you along and allows you to take advantage of whatever your past self prepared for you.
That's a fun one! So much depends on the mechanism of action, so I'm going to assume that you get to pick a couple lessons that you can embed as subliminal imperative for future me. One would be a bias for action, get shit done now, don't put it off! Two would be an impulse to ENJOY exercise! And third would be a reminder that the happiest times in life are always with people you love enjoying each other's company; and being able to create those circumstances comes from creating an atmosphere of acceptance, friendliness and love. SO DON'T BE A DICK! 😉