Crowns is the swedish currency, three crowns is also the official heraldic national symbol of Sweden. And, not to forget, the nickname of our national hockeyteam.

Since it's a restaurant it may be a play on words. Kronor has (at least) two meaning, one being the Swedish currency, the other meaing the head dress of kings and queens.

Three crowns have long been an official symbol for Sweden. I think it's a few hundred years old, from the times when Sweden and it neighbours kept concering each other. At one point Sweden ruled over 3 countries and the symbol was established. The background is blue and the crwosn are yellow (Swedish colours). One crown is above the others, like a hirarcical structure (possibly to show the one country ruling the other two).