(read how to identify your stamp below)
You have the 6¢ Lincoln from the years 1870-1882. It is fairly common
If the stamp has a grill embossed on the reverse of the stamp (shown below) click here.
If the stamp has no grill embossed on the reverse then examine the bottom left corner of the stamp.
On the bottom left corner the four left most lines of the ribbon have thicker shading. Below this text there are two images, one showing the thicker shading and one with normal shading.
If you see the thicker shading in the ribbons, as shown below then click here on the menu to the left. If the stamp has a date cancel and you can see the date is prior to February 3rd, 1879 then click here. All unused stamps belong to the latter period of numbers 182-191.
If you do not see the thicker shading in the ribbon (shown below) then click here.
Lastly look at the lines that border the image. If there are only three lines, as shown below, they you have the 1882 printing by the American Bank Note Company. The value of these can be found by clicking here.
Normal shading inside ribbon
Three border lines
Four border lines
This stamp was reprinted in 1875 and it can be viewed by clicking on the numbers 167-177. These are all accounted for, so you will not own this.