The flat press 10 cent motorcycle stamp (Scott E12) that debuted on July 12, 1922 was replaced by the more economical-to-make rotary press 10 cent motorcycle stamp that debuted on Nov. 29, 1927 (Scott E15). The early grey violet color of the rotary stamp would shift to more of a red lilac color as time would go by. Whenever I view the E12s on eBay, I am always amazed by the number of red lilac motorcycle stamps that have been incorrectly identified by their owners as E12s. Besides the color, the rotaries are perf. 11 x 10.5 rather than perf. 11 and are slightly taller vertically.
The above E15 FDC is another Hammelman typewritten cover.