It has been used as the symbol is correct here. Use present perfect when the action referred to started in the past, and either continues (or continues to have relevance) at the time of speaking. To me, used to and used for are incompatible, as shown in the examples below. However, i am unable to substantiate this. Ms word doesn't see the differences, so i turned to.
Does to be used of mean to be used for: Wikipedia the english term empiric derives from the greek word ἐμπειρία, which is cognate with and translates to the latin experientia, from.
