Nope, that is the "Filled S" aka Type 1 mint mark. Clear S is a bit of a misnomer for the 1981 issues. The "Filled S" for the 1981 is actually the Clear S for 1979. The Type 2(clear S) in 1981 has bulbous serifs and round loops in the S.
Here is a nice set of pics for 1979 and 1981. Type 1 and Type 2 work better for these but "Clear" and "Filled" seem to be stuck in the vernacular.