Pieces from the same pottery works may carry different backstamps depending on who commissioned the work. There are also large numbers of fake backstamps which are very hard to detect.
Alternate meaning: In stamp collecting a backstamp is the mark of any postal station the cover (envelope or package) traveled through en route to its destination. It was often a mark used to denote time in transit. The backstamp is usually applied to the back of the envelope, but may appear on the front depending on postal regulations.
Some Pottery Backstamps: