What’s the little gold thing you get in the rewards after a scene (looks like what you twist on the..

That's a turn key. Earn keys when the Detectives Needed Challenge is active to get rewards. When it's active, you'll find a stopwatch icon on the right upper area of your island scene. Tap on it to find your progress, the rewards, the time limit, and whether keys are earned from playing scenes or completing Help Wanted cases or both.