The Brief: "Chain" is slang for a gold or silver chain necklace.

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“Chain” is slang for a gold or silver chain necklace. A chain is a status symbol, particularly in rap and hip hop.
Don’t look rich, I ain’t got no chain (huh) – Chance the Rapper, “No Brainer“
2 chainz’s name refers to his signature two chains (or more) which he wears.
I wear every single chain, even when I’m in the house – Drake, “Started from the Bottom”