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.
@WINTERBEAR, The marks for this piece are not the standard marks for Dedham commercial ware. This type of vase was experimental. Robertson from 1895 to his death in 1908, was experimenting with different glazes and these vases were never meant for sale to the public. The majority of them were part of the factories museum collection. When the company went belly up in 1943 the stock of experimental pottery was bought up as war surplus and retailed through Gimbles Department Store.