Ornate 12 inch silver round pedestal platter, marked 1759

This round, flat 12 inch plate or tray has a 1 inch high pedestal and is ornately edged with leaves & grapes on a vine.  It has a floral design that is visable on both sides.  The stamped marks are a shield containing a crown eminating an arm holding an arrow or spear.  There is an 's' beside it.  There is also some info scratched into the silver:  "1759", "12 1/2", and "122qo" over "R- H /-" .  I would like any info to help identify the maker, age or any history about our heirloom. 

Good