In The Gilded Six-Bits, Joe Banks symbolizes several things. First he symbolizes domestic happiness. He demonstrates what it feels like to be genuinely happy in a marriage and to be fulfilled in the role one chooses for one's self, in the role one has invested one's self in. He greatest joy in the day is to go home to his beautiful wife.
Then Joe Banks comes to symbolize naieve captivation with the lure of glitter and show as depicted by Slemmons, a type of living that is antithetical to the genuine life Joe Banks has with Missie May. Joe makes the mistake of making a risky investment in trying to fall in with and impress Slemmons and loses some of his riches.
Then Joe comes to symbolize true forgiveness, hard-won but still true forgiveness. When Missie May gives birth to a baby who looks wholly like Joe (and Slemmons) he can believe that their rich life can be reclaimed and rebuilt.
As Joe's symbolic representations indicate, the symbolism of Joe Bank's name relates to true riches in life and what in life is worth investing in and what is the empty show of risky scam investments. In other words, he symbolizes the true values in life and the source of true happiness.