Display towels
Just like the crockery set that you only ever get out if the Queen is coming to visit (or your mother-in-law), the towels that are for guest use only are an important component of any household dynamic. Knowing which ones are which is key to avoiding an argument.
I don’t know why we feel the need to have special towels, soap, or even toilet rolls in the house that the actual members of the household aren’t allowed to use. It’s as if we think that all our guests judge us on the state of our bathroom accessories when really it’s only our mother-in-laws that do that.