An indicator for a quick coupler for the mounting of an attachment to an earth working machine. The indicator (10) has a sensor (14,15) which, in response to movement of a movable pin engagement component (F) of a coupler (A), determines that the pin engagement component (F) will have moved sufficiently to engage and lock a pin (P2) of an attachment with the coupler (A). The indicator (10) has an indicating part (17) which is caused to be moved in response to the sensor (14,15) to thereby provide a visual indication (25) that engagement and locking of the pin (P2) has occurred.