Rules vary by hotel, but if I left a loose fifty bucks in a room when I stay in one, I wouldn't count on ever seeing it again.
The policy in hotels that I run is, if a housekeeper's 'tip' is over twenty bucks, she must tell us, and turn it in. We'll let her keep twenty bucks of it, and hang on to the rest in accordance with the usual lost and found procedure (thirty days). If the guest calls with a credible story (as in, he or she names close to the correct amount of money left behind) about how he left loose cash in the room, we send a check to the guest for the total amount we found, and we take the hit on the twenty bucks ourselves and let the housekeeper keep that part (we don't want to supply an incentive to dishonesty, or a disincentive to honesty).

If it's in a wallet, there's no question: any indicator that it wasn't left for the housekeeper intentionally by the guest means that it all belongs to the guest. We handle it in accordance with our usual lost-and-found procedure. (With wallets and other things of obvious value, we don't wait for a call: we contact the guest.)
Back in the day, tipping the housekeeper was as to-be-expected as tipping a waitress. Large chains and franchise organizations have gotten away from it (you can still order tip envelops from a hotel supply house, but chains and franchise organizations forbid the use of them.) Hotel owners went right along. Tips present a management challenge (disputes arise over how to divide them if more than one housekeeper services the room over several days, and any room attendant with any 'seniority' at all demands the 'right' to pick and choose what rooms she'll clean, and we'll get to some others . . .)
The policy in hotels that I run is, if a housekeeper's 'tip' is over twenty bucks, she must tell us, and turn it in. We'll let her keep twenty bucks of it, and hang on to the rest in accordance with the usual lost and found procedure (thirty days). If the guest calls with a credible story (as in, he or she names close to the correct amount of money left behind) about how he left loose cash in the room, we send a check to the guest for the total amount we found, and we take the hit on the twenty bucks ourselves and let the housekeeper keep that part (we don't want to supply an incentive to dishonesty, or a disincentive to honesty).
If it's in a wallet, there's no question: any indicator that it wasn't left for the housekeeper intentionally by the guest means that it all belongs to the guest. We handle it in accordance with our usual lost-and-found procedure. (With wallets and other things of obvious value, we don't wait for a call: we contact the guest.)
Back in the day, tipping the housekeeper was as to-be-expected as tipping a waitress. Large chains and franchise organizations have gotten away from it (you can still order tip envelops from a hotel supply house, but chains and franchise organizations forbid the use of them.) Hotel owners went right along. Tips present a management challenge (disputes arise over how to divide them if more than one housekeeper services the room over several days, and any room attendant with any 'seniority' at all demands the 'right' to pick and choose what rooms she'll clean, and we'll get to some others . . .)