If memory serves, it is the oversized, mainly black and white stamp you are asking about. If so, sorry to say, but you can use it on a letter. If it is used, even less value.
Six cents.
6 cents
This is a very common stamp - practically worthless used. Worth face value mint if you need it for postage or if you can find a collector who wants it for his collection. A dealer would charge up to 20 cents for it.
This stamp made in 1968 is worth 20 cents used and 40 cents unused.These stamps were not made in 1734.
{| |- | I don't find a 6 cent Wildlife Conservation stamp, though there is an 8 cent set. You can purchase these for 20 cents used or mint from a dealer. This minimum value indicates that it has no real value. Dealers typically will purchase stamps at around 25% of the catalog value. Consult a stamp catalog such as Scott's, for a description on how stamps are rated and graded. |}
The Eisenhower 6-cent stamp was issued on March 24, 1969. It was part of a series that honored the 34th President of the United States, Dwight D. Eisenhower, who served from 1953 to 1961. The stamp featured a portrait of Eisenhower and was released as part of the Postal Service's commemorative stamp program.
In mint condition a 6 cent stamp is worth 6 cents (maybe less) for common US postage. However, the collecting value can vary considerably, there are a very few, very old stamps that are worth hundreds of dollars. Most however are going to cost a few cents and the sale value will be small.
There were three 6 cent Christmas stamps. They have the Scott catalog numbers 1363, 1384, and 1414. They all have a catalog value of 20 cents, mint or used.
This was issued December 6, 2006. It has a face value of 39 cents.
That is Scott Number 1382. It has a minimal value and can be purchased for about 20 cents.
The cost of a First Class US postage stamp in 1968 was 5 cents. It was raised to 6 cents on January 8th. It stayed at 6 cents until 1971 when it went to 8 cents.
They do have some value for collectors. And if they haven't been used, they can still be used to mail a letter, with the addition of value to the current rate.