Scott Catalog # 4548 - 4551 / FDCO Exclusive First Day Covers.
Set includes: 4548 Clipper Ship / 4549 Auxiliary Steamship / 4550 Liberty Ship and 4551 Container Ship.
The Collectible First-Day Digital Color Postmark is an official digital postmark bearing the first-day-of-issuance-date containing an image that relates to the stamp design with the words "FIRST DAY OF ISSUE."
The cachet (image) was made on a computer and printed on high-quality envelope.
