Early American Pottery Mark - iS (or Si)

by Leon Carbonaro
(Danbury, CT, USA)

Hi,

I have this nice small pottery vase -- drip glaze in blue and green -- well done and nice shape.

I would like some help in identifying the mark that is in a small rectangle with the letters "IS" or maybe "SI" if you turn it upside down.

Pictures are attached.

Thanks for the help.

Leon.