What the check proves
Four things, every time.
Signed
A digital seal added the moment it's issued.
Tamper-evident
Change one character and it fails.
Expirable
Every Signal carries an expiry date.
Revocable
The learner can switch it off any time.
What you get back
The proof is public. The person stays private.
✓ / ✕
Valid or invalid
Date
Issued on
Date
Expires on
None
Personal data returned
Real cryptography (Ed25519, checked against published keys). The sample learner is fictional. Developers can run the same check from the command line — GET /api/v1/signal/verify, CORS-open, no key.