It's not enough to simply have a dream sign. You need a common recurring dream sign that is easy to recognize. Then it is easy to become lucid.

If you go over your dreams you would notice that there are at least several dreamsigns that you may be seeing, but you wouldnt recognize them as dreamsigns because you see them a couple weeks apart or so. And that is not enough to successfully induce LDs....


As for creating new dreamsigns I had a several bizzare experiences with the following dreamsign - in the middle of a dream I would interrrupt the flow of a dream and ask DC a question like "why do I dream?" " why am I here?" "what is knowledge?" and so on.
The act of asking the question is not lucid, but it instantly produces lucidity as it is just way too out of place.
If I recall correctly this was caused by philosophically thinking about LD experience and actually planning to ask DCs these questions.
This is a unique dreamsign because it originates from within the consciousness present inside the dream. Since your consciousness is always there it theoretically can be said that this dreamsign can be developed into a very reliable way of becoming lucid.

I think I will conduct some experiments on the subject...