A box office is the gate between the street and the show, so it is read as the price of entry to something you want. Sold-out signs stand for feeling left out of an experience.
Has this come up in your dreams before? What was going on in your life then?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.