Another official mark, but like the Duty mark (1784-1890), strictly speaking, it's not a hallmark, but a mark applied by the Assay Offices by order of the British Government.
This mark, two intersecting circles within a rectangle, was struck on a certain type of item. The Government also issued strict guidelines as to how the item was manufactured.
The mark was in use for eleven years.

What item was this mark used on? What were the dates of its use?
Trev.