Recently there was a post about personal information contained in guest folios not completely pushed under the door. A great post by the way.
As a suggestion perhaps the folios, if they continue to be given to guests in their rooms, be stripped of all personal information. If the receipt is what is required for reimbursement for company travel this might be problematic but there's always the fully complete one available from the front desk.
The bill would just be the bill and could be on a much smaller piece of paper, merely identifying the room number and the charges, with no additional information.
Perhaps I am missing something. My last two bills (which I happen to have handy) have only my first initial and last name lumped together, my CC with only the last four digits showing and my MR # with only a few digits showing. There is not enough information on there for anyone to know much about me. They could deduce I am a member of the MR program and I use a certain CC, but neither would get them very far. They would stand a better chance of being able to hack into the computer system of the hotel and gain info than to get it by grabbing a paper bill slid under the door. My $0.02.