What does Al Capone's "Your Turn" Note represent?

Al Capone’s “Your turn” note symbolizes the dangers of dealing with convicts as well as underscores Moose’s dad’s life lesson that one should always shine one’s own shoes – and not owe favors to other. After Al Capone gets Natalie into Marinoff, he sends Moose a note reminding Moose that Moose now owes him. As it turns out, Al Capone wants only yellow roses for his wife – but the request Capone could have made of Moose could have been far worse, not to mention the consequences of Moose failing.