(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.
THE IMPERFORATE VARIETY (no perforations on the stamp) is #611
THE PERFORATED VARIETIES
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.