Romeo is a yellow cross laid over a red background, and it stands for "R" in the signal flag alphabet. Like his counterpart Juliet he is ironically colored, although you should keep this fact to yourself too.
NOTHING! HA! Poor lonely Romeo. If you see someone flying this alone you should just ignore it completely. If there are numbers on there they indicate range in nautical miles, another way for Romeo to quantify how lonely he is.
Check out the rest of our Signal Flag explanations!