Symbolism, Imagery, Allegory
We're first introduced to the gilded six-bits when Joe describes Slemmons to Missie:
"He's got a five-dollar gold piece for a stickpin and he got a ten-dollar gold piece on his watch chain […]." (48)
Impressive, right? Wrong. Soon after pointing him out, Joe catches Slemmons in his house with his wife and then:
Joe found himself alone with Missie May, with the golden watch charm clutched in his left fist. (76)
Funny how quickly things can change.
A few days later, Missie (and readers) realize that the coin, like Slemmons, is not what it seems:
Alone to herself, she looked at the thing with loathing, but look she must. She took it into her hands with trembling and saw first thing that it was no gold piece. It was a gilded half dollar. (101)
This moment is a big reveal; everything that Joe thought about Slemmons, is a lie.
The six-bits is a symbol of deception. It's also used by Hurston as a warning that appearances are not always what they seem and that both Joe and Missie made the mistake of thinking that money leads to happiness. In the end, money almost drove them apart and it takes something non-material (love, a baby) to keep them together. If you're unclear on what exactly a six-bit is, check out this really detailed explanation from a coin collector's magazine—a six bit is equivalent to about 75 cents. Big money, right? Wrong.