What is a slot machine's highest paying symbol?

It depends upon which slot machine you are referring to. On many older and some newer slot machines, the jackpot symbol is a red seven. However, many slot machines today use a variety of symbols. Check the paytable on your favorite slot machine to determine which symbols have the highest payout. Keep in mind that many games now have bonus features (free spins, etc.) that can generate cumulative payouts far exceeding what the highest paying symbols might pay by themselves.