Soda Crate Moral Dilemma (& Informal Survey)

I took a walk today and found a brand new paper cup with "McDonalds" clearly imprinted on it. This thread has me now thinking I should return it promptly. But I have a new dilemma. McDonalds are all franchised. What if I returned it to a franchisee who didn't lose this valuable paper cup? Would I be implicit in unjustly enriching that franchisee? Does McDonalds award franchisees for efficiency? If so, not only would the franchisee I mistakenly returned the cup to be reaping the benefits of a free cup, but the other franchisee would not only have lost the cup but they also would now be lagging the other franchisee due to that franchisee gaining an undeserved cup. The franchisee who lost the cup would actually be further damaged by my good moral actions. And what if the cup was actually the property of a customer who purchased a drink and painstakenly kept it in mint condition only to have it returned to the seller rather than them? Would they feel that the world conspired against them since they legitimately purchased a cup only to find that it actually was returned to the merchant rather than to them. What if that was the final straw that sent them into a downward spiral of depression, leading to them contemplate taking some kind of drastic action, like wearing white before Easter.
Perhaps I should have just left that cup on the ground.