It's not really a hint. It's just instinctive. When you want to get closer to someone, you find every excuse to get closer to that person. There is no hinting about crushes. Girls in general do not wink, or stare or 'look passionately' at someone. It just happens.
You see, attraction and relationship is a battlefield. Why does Ai-chan call it a battlefield? Consider the following scenario.
1) The Kingdom of Sara and the Kingdom of Susan has always been good friends, but one day, Sara feels that they can be even closer. Queen Sara is sexually attracted to Queen Susan, but Queen Sara doesn't know how Queen Susan feels about her and is afraid that if she propose that they commit to a no-holes-barred alliance, Queen Susan will freak out and cut ties with her. So what does she do?
Queen Sara then signs a trade treaty with Queen Susan, and with that, learns how much Queen Susan is open to the idea of mutual cooperation. Another year, they sign a defensive treaty, where they cover each other's asses with their hands and stare longingly at each other when nobody's looking. You see, for you to know the signals, you must put your foot forward and meet them halfway. If Queen Sara did not put forward that trade treaty, maybe Queen Susan, the shy girl she is, wouldn't suggest it either. As a result, neither know of each other's feelings.
Of course, at some point Bitch Queen Marisa would try to get in the way and put forward a more favourable trade treaty to lure Queen Susan away. But as long as Queen Sara puts in the effort to keep Queen Susan close, and treats her well, there is not much chance that Bitch Queen Marisa can succeed. And the rest is history.
All you need to know is that there is no 'special hint' for a relationship. You need to meet the other party halfway. Both of you needs to make an effort to take a step forward towards each other.