very interesting, I am sure you looked this up but since I had no clue here is the markings section from wikipedia for others to learn as well
chris
1892-1895: C.P.U.S. (Chelsea Pottery U.S.) impressed inside a clover leaf.
1896-1928: Square blue stamp with DEDHAM POTTERY printed over a rabbit; impressed foreshortened rabbit beneath.
1929-1943: REGISTERED added under standard Dedham Pottery stamp; two impressed foreshortened rabbits beneath.
Rarely the decorator would add his initials, a date, or the initials of the purchaser but these instances were rare and therefor, for collecting purposes, valuable.
Maude Rose Davenport a very skilled decorator at Dedham Pottery between 1904-1928 signed her work with a rebus, a small 5mm circle in the border of her designs.
Hugh C. Robertson sometimes signed his decorations with a square.