There's a good chance that is a "forever" stamp, meaning it will cover the cost of postage for an envelope, even if the price of stamps increases.
It can also be a stamp printed by the post office for an upcoming rate increase. Since they don't know exactly how much will be authorized, they mark it 1st Class Postage and then can sell it at the appropriate rate. This link below will tell you the designs.
The US Postal Service has a list of nondenominated postage on their website in pdf format Linked below.
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Some nondenominated stamps are "forever" stamps and the value is whatever the current price set by the post office. In the US, they will have "Forever" written on them rather than a denomination.
In Canada, "forever" stamps have a small maple leaf w/ a P where the price usually is printed. The word forever doesn't appear on the stamps.
Forever
The current value for a standard postage stamp is 46 cents.
The F series stamps were issued in 1991. The postage stamp has a face value of 29 cents.
Face value of the original stamp was $0.20
The stamp-postage value of a stamp is visible on the front of the stamp.
The face value of the D stamp was 22 cents when issued in 1985.
15 cents.
96214455 doollars
value of silver stamp holder
Face value only
15 cents
it is 44 cents now