This mystery topmark has been discussed on a couple of online forums, but no one has been able to figure out who or what J.A.R. & Co. was, and with no backstamp, its manufacturer is unknown, too. With the Art Nouveau style of the monogram and the addition of the Nouveau Katy Ornaments pattern around the rim, it would seem to have been made in the early 20th century.
The creamer is about 2 ¾” wide by 2 3/8” high. It is in excellent condition with only light use marks, though you can see that the green lines show some wear.