Silver was stamped STERLING (with some variants of this) in Cork, Limerick and Kinsale from circa 1710 and common from 1715, along with the maker's mark, although you can find silver with just STERLING and no maker's mark or vice versa. Ireland however was not the only country to stamp STERLING so other factors need to be examined too. If the stamp is in script letters rather than block, it's likely American.
It's impossible to say any more without photos of the spoon. Refer to: http://www.925-1000.com/images.html