I'm not sure specifically as there could be many novels with this title or related concept. It might be about different ways people show affection in a fictional story, perhaps romantic love, friendship love or family love shown through the characters' actions and relationships.
A sign of affection novels often focus on the development of a deep emotional connection between the main characters. They might include small gestures, meaningful looks, and shared experiences that build up the romance. Also, the writing style is usually descriptive and evocative, making readers feel the intensity of the affection.
I don't know as I haven't read it. It could be a young couple if it's a romance - like a boy and a girl who are trying to understand their feelings for each other through signs of affection.