The black market stands for needs met in the shadows, outside what is approved. Tradition reads it as a part of life where you go around the official way because the official way does not serve you.
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.