There was a sign in front of my seat: No Smoking. I'm also the office manager, ho ho, really.
Just kidding.
You can put a motto or aphorism you like, usually four words, to express your attitude and ideas. The key is to express your true inner feelings, attitude towards life, and views on cultivation.
For example: be virtuous, be modest and prudent, be considerate of all the talented people, be cautious in independence, pool your brains, be strong without desire, be like bamboo or pine, etc.
However, generally speaking, the characters are usually not hung behind the body. There is a saying of "carrying the characters". They are usually hung on the wall facing the host or the wall facing the guests. If you face the north and the guests sit on the west side after entering, you can hang the words on the north or east wall. The purpose is to alert and encourage yourself, or to express your attitude and opinions to the visitors.