Apparently people don't know. But there are pillows that have a yes and no side that a wife will flip depending on if she is up for having sex that day. I doubt they are actually used unless ironically, but it's a fun trope in media.
@Doctor_Malsyn The pillows exist but they're more of a gimmick. The actual pillows have "yes" on one side and "no" on the other. They're intended for married couples and the sort who are sleeping in the same bed all the time but that doesn't mean they're getting it on every night. Putting the "yes" side up is supposed to express interest while "no" means not tonight.