The dream plot often is forwarded along by very unusual events (e.g. suddenly the room turns blue and everyone disappears).
Other times, a cryptic message works its way into the dream event.
Often the code is symbolic rather than alpha-numeric, though it can be either.
Other times, it is a riddle.
Whether or not you can decode the message becomes the dream conflict.
If you can decode the message, does it mean anything to you?
It may make perfect sense to you, but mean nothing to others in the dream, or vice versa.
The point is that the message was decoded, showing insight.
The relative meaning lies in whether or not the insight can be appropriated by the dreamer.
If you cannot decode the message, you may be experiencing life as incomprehensible at some level.
This dream reveals that truth of your conscious life.
The key is to look at who in the dream serves as a source of knowledge about the code.
Who gave you the message?
What was the reaction of others is when they learned of the message?
Are they worried for you, nonchalant, or joyful?
