(read how to identify your stamp below)
You have the 2¢ Harding from the years 1923-30. It is a somewhat common stamp with perforations and less common without perforations. Their are two varieties of the stamp with perforations, to tell them apart count the perforations along the top or bottom, as shown below. Either they will have 10 or 12 perforations.
The 10 perforation stamp is #612 and the 11 perforation stamp is #610. Both can be found by clicking here.
There is one other variety, that is a rotary press perf 11 (#613). As they are extremely scarce and will always be accompanied by a certificate I have not included it in this identification guide.