So I found the below set of 1 Cent Postage Due stamps in some unsorted ones I have. A quick search on the internet said that these may be somewhat rare. How do I verify if they are real or not though? Any help is appreciated. Thanks.
Have you determined their watermark yet? It should be easy with a block of four. Aside from that the only difference would be color. To me they look to be the more common color, but the internet is not a reliable way to verify what color stamps are.
