A railway signal is read as permission to proceed or a call to wait. Dream books link red and green lights to how freely you feel allowed to go ahead with something in waking life.
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.