Can someone please help with the maker of this plate????

[summer_nite]

This plate caught my eye at an Estate sale - but - I know nothing about silver. A friend has told me one of the marks is a leopard with crown - crafted in London England prior to 1822, next three marks look like triangles to me - is the silver content - and then looks like a fat S dates it at 1733....Would anyone know the maker of this and if these marks seem concurrent to each other and the art work....Is this plate a common piece?? (edit - see guidelines) I hope someone can help with my questions.... I really appreciate your time......