From what I understand, a dream sign is something that is consistent throughout most, if not all of your dreams. Like, for instance, if in every dream, you have a purple dog singing a song in a top hat and cape, you can probably say it's a dream sign.

And I feel your pain, bro. I'm just starting out myself, trying to locate mine. They're elusive though, it's like playing a game of where's waldo? XD