Yes, it does.
For a self-adhesive stamp, no it should not be removed. Mint means it is still capable of being used for postage.
This stamp is Scott # 1391. It has a catalog value of 20 cents mint or used.
The "S" is a mint mark not a stamp, but the value is $2.00-$3.00 for circulated coins and a mint state coin is $7.00
The Scott catalog number for this stamp is 2137. The breadwagon stamp was not issued in 1866, it was issued about 1981. The item pictured was made in the 1880's. The stamp has a minimal value used and can be purchased for about a dollar mint.
Mint - face. Used - nothing.
You can consult a stamp catalogue at your local library to identify the year and condition of the item with an estimated value for it.
The value of stamps is determined by their value and rarity. The value for a 1993 Elvis Presley complete stamp collection in mint condition is between 99.00 and 130.00 as of 2014.
Mint and used are worth about .20cents
You can purchase a mint set of all 29 1980 stamps for around $26.10.
That is Scott Number US 1897A. It has a catalog value of 20 cents mint and 20 cents used.
It is a common stamp worth 10 cents in mint condition.
.90 c mint .25 c used