The legend is that if you invite a lady for the night, it's so you and she can keep an eye on each other, in case either is worried about one going through their stuff/wallet while the other is in the bathroom.

I stayed in such a hotel, and getting up to go the bathroom I noticed someone had flicked a business-card-sized advertisement under the door, for said companionship...

Hotel safes are a much simpler solution to this problem...