What you describe is a registration lozenge.
Making it that the design of your piece was registered in June 1876.
Under the III there should also be a number, that will give the day in June when the design of the piece was registered.
Should the number be a 6 or 14 then the registration belongs to Whittingham & Percival, Manchester.
For the rest, I am sorry, I cannot help, but maybe others can.
A picture would also be nice.