Suppose someone publicly claims appointment by a king and asks the king to perform a distinctive act understood by the audience as endorsement. If the king repeatedly performs the act, the audience can recognize the appointment.
This illustrates three distinct things: the claim, a confirming sign and the audience's resulting knowledge.
The analogy has limits: divine action is not subject to human compulsion or need. It illustrates only how a properly situated, authoritative sign can provide evidence for a claim.