The B stamp is worth a face value of 18 cents. There have been several non-denominated flag stamps. They were used to cover increases in postal rates when they weren't sure how much would be authorized. Check the US Postal web site for specific pictures to match up with the one you have.
Three stamps were issued and there are 4 values for each issue. This stamp is Scott Catalog # 1818, 1819 and 1820, a regular issue that was issued in 1981. 100's of millions of stamps were issued.
The values are:
Scott Cat. # 1818 (sheet)
New = 35 cents
Used = 20 cents
Face = 18 cents
Dealer value = 15 cents (20% below Face value)
Scott Cat. # 1819 (booklet)
New = 40 cents
Used = 20 cents
Face = 18 cents
Dealer value = 15 cents (20% below Face value)
Scott Cat. # 1820 (coil)
New = 40 cents
Used = 20 cents
Face = 18 cents
Dealer value = 15 cents (20% below Face value)
(Scott Specialized Catalog of US Stamps, page 121)
15 cents
That stamp was issued in 1985. It has a face value of 22 cents.
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.
The B stamp pictures a stylized eagle. It has a value of 18 cents. You can still use it for 18 cents worth of postage.
15 cents.
96214455 doollars
The purple B stamp with eagle has a face value of 18 cents. It can be purchased for about a $1 mint and .20 cents used. It's a pretty common stamp so the value has never gone up. It was issued in 1981 and cat# 1818 if you want to look it up on Ebay to make sure we are talking about the same stamp.