(v)To literally tuck your chain or medallion underneath your shirt for protective reasons. So as not to get snapped off your neck by thugs.
(adv)Describes a rough situation or neighborhood that you would want to watch your back while being in.
An expression that stresses the ghettoness or thuggery of a club/neighborhood/situation.
Fat Joe uses it frequently.
An friend would tell another friend to "Tuck yo chain" if they were about to enter a club or situation that has thuggish characters that would be interested in stealiong your chain.