Kingdom Hearts II Roxas Day 6

Crown's definately for Sora. Other symbols,as has already been suggested, may purely have been a way to introduce the Nobodies as a third party.

 

Another thing to consider is, what do you think of when you hear the word: Crown?
King/queen?
Kingdom?
Kingdom Hearts!
I think the crown necklace Sora wears is meant to just be a discreet little connection between it (it doesn't necessarily have to mean anything like, oh Sora is royal, cause I doubt that is it lol).
But yeah, it is safe to say that the crown Necklace is one of the things that people recognise with Sora, after all, he had it in KH1 and it's the only item of clothing (accessory) he kept when his clothes changed. So I do believe the crown symbol drawn is meant to represent Sora.
After all, in the secret end of BBS, they said everything is connected through Sora, he is the key to it all. So he would be important enough to be symbolised in the drawing.
There is also the fact that Roxas has a connection to Sora (well, of course lol).
And the link of Roxas to Sora is the fact that Sora (Crown) became a Heartless (Heartless Emblem) and therefore created Roxas, a Nobody (Nobody Emblem).
There are many things it could be, but I don't think it's meant to be anything particularly important or thought about. It's just there. (Of course, we CAN and are thinking about it lol, but I don't think that was Nomura's intention at any rate)

Wow... I sure rambled on... lol

 

Another way of looking at it then is that the entire drawing itself signifies Roxas's existence if you look at it from how I mentioned it.

 

There is a piece of paper to Roxas' left. If you look closely at it, it seems to have something on it. I think maybe that is how he knew what to draw. Because it was already on that paper and he just copied it.

 

Yeah, that is the sheet he got from Namine's sketchbook in the white room that one scene before he entered the library and had to draw the symbol.
Namine etc must have known he'd need it, whether it's because they wanted to lead him to Sora or what... it doesn't matter really. Point is, that's how he got the paper and knew what to draw.

 

lol I never really paid attention to what he drew on that table XD great observation though. And I agree with the other people that the crown might symbolize Sora. Since he's the one slaying Nobodies and Heartlesses.