A megaphone is read as the wish to be heard by many and to amplify your voice. Dream books also link it to feeling ignored at normal volume.
When this appeared in your dream, what were you feeling?
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.