The foghorn stands for a warning that carries when nothing can be seen clearly. Dream books read it as an inner alarm, a call for caution, or a voice guiding you through uncertainty.
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.