SBA for Susan B. Anthony
s.b.a.
It's the monogram of Frank Gasparro, who designed the coin.
The letters you see on the back of the coin are the monogram of Frank Gasparro he designed the reverse. Gilroy Roberts designed the obverse his monogram is on Kennedy's neck.
It's the monogram of Frank Gasparro, who designed the coin.
It's technically "A W" and is the monogram of A. A. Weinman, the coin's designer.
The FG on the reverse is the monogram of Frank Gasparro, he designed the reverse of the coin
It's the monogram of Anthony Di Francisci, the coin's designer.
If you mean the BLP, it's the designers monogram Bela Lyon Pratt.
It's the monogram of the coin's designer Anthony de Francisci, all Peace dollars have it. The 1923 Peace dollar is a very common coin, circulated examples are $37.00-$40.00.
"BLP" is the monogram of the coin's designer, Bela Lyon Pratt. There's more information at the Related Question linked below.
From your description the coin is a common Susan B. Anthony dollar (1979-1981 & 1999) that is in circulation today. The FG is the designers monogram and adds nothing to the value of the coin. It's just a dollar coin, spend it.
You may be seeing an intertwined A and F on the coin's front. That's the monogram of the coin's designer, Anthony (Antonio) de Francisci, which is below Miss Liberty's neck on the coin's obverse. An "L" in any other place was probably added after the coin left the mint.