A serial number marks one item in a long series, so it is read as anonymity, or as the question of what makes you authentic and unique. Dream books also see in it a feeling of being one of many.
Where in your waking life have you met something like this lately?
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.