This is a First Day Cover that has been hand signed by the great, Bert Blyleven. The cachet has been authenticated and slabbed by PSA/DNA. The serial number is verifiable online using PSA/DNA #84092231. The cover comes encapsulated in a tamper-proof cover. 100% authentic signature from Minnesota Twins legend, Bert Blyleven. A great gift idea for a Minnesota Twins or MLB collector.