That would be Scott number US 1015 issued in 1953. A mint copy can be bought for 40 cents and a used one for the minimal 15 cent cost. Consulting a good catalog will help you properly identify the specific stamp and find an estimated value for it.
15 cents.
15 cents.
44 cents in 2012
20 cents.
The C stamp came out in 1981. It has a face value of 20 cents.
They are probably worth 9 cents.
four cents
four cents
5 cents.
50 cents
They're worth 8 cents each.
5 cents.