An ashtray holds the remains of something already burned through. It is traditionally read as habit and leftover tension, and an overflowing one as worries that have been put off rather than cleared.
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.