One miracle? OK - everyone in the world wakes up on the same date with a tattoo that spells out in the local language “Hi, this is Miracle Worker with a message for you - Have a nice day.”
This makes it personal - someone with any pretention to sanity can’t claim that “It’s a fake because I didn’t see it.” And in the aggregate so impossible that it has to be recognized as a phenomenon outside of the regular course of nature.
Or maybe the message should be “Hi, this is from I once was a Miracle Worker - I’ve shot my wad with this message.”