Mothballs keep things stored and unchanged, so the symbol is read as putting a plan, a feeling or a part of yourself on hold, preserved but out of use.
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.