The motive of a crown can be shown in many different ways, but one has to notice that this particular one comes with exactly three spikes.
The number three is after seven and thirteen the most used number in the series aka the main characters being organized in trios, there are
three main trios in the series etc.
The crown is also used often for in-game items like Puzzle pieces (in KH 2 FM), stickers (in BBS), the top of the cards in Castle Oblivion (CoM) or some accessoires as well.M
More hints at the crown having something to do with KH itself and Sora (at least thematically) can be taken from that when Sora opens a Gate to the Lanes Between in KH 2, a large glowing crown appears beneath him while the outer Symbols of his own Heart Station in the awakening are all crowns.
Another particular interesting issue is this symbol:
It is found in the Old mansion in Twilight Town and displays the crown at the bottom going into a heart (in the middle spike) which is then crowned with a fleur-de-lys.
The crown is displayed on the outer circles of Sora's awakening station, which is as we know a representation of the heart.
Well, the fleur-de-lys appears also often and in more various forms during the entire series, but there's one interesting occurrence to take note of in connection with this symbol.
In one of Ventus' awakening stations (the first one after Sora helps him) the outer symbols are filled with...yeah, a fleur-de-lys:
More fleur-de-lys symbolism with Ven exists, i.e. when examining his Lost Memory-keyblade, as well.
A crown and a fleur-de-lys connected through a heart...I won't actually place judgement if it was done intentional or not, but that symbol clearly
can be interpreted as showing the connection between Sora's and Ventus' hearts.