A hard hat stands for protection while doing demanding work. Tradition reads it as readiness for a tough phase and the wish to shield your mind from strain.
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.