In Christopher Paul Curtis's young reader's novel Bud, Not Buddy, one reason why the title character Bud believes Herman E. Calloway to be his father has to do with his mother's reaction to a flyer upon which his name is printed.
His mother used to keep flyers of show announcements, and Bud has kept those since her death. Bud describes that one day she brought home a flyer announcing, "Direct from an S.R.O. Engagement in New York City ... Herman E. Calloway and the Dusky Devastators of the Depression!!!!!!" (p. 6-7). He further narrates that the day she brought home the flyer and laid it down on the dinner table, she looked very upset; she "kept looking at it and picking it up and putting it back and moving it around" (p. 8). He also informs his readers that not long after she brought home the flyer, he opened her bedroom door to find her laying dead, having committed suicide. Hence, from the clue of how upset the flyer made her, he concluded that an important name was printed on the flyer, most likely the name of the father who had abandoned him.
In Chapter 9, Buddy later explains to his reader exactly how his idea that Calloway was his father developed in his mind. He had been being persecuted by Billy Burns in the orphanage, who was making fun of all the orphans for not knowing who their parents were. Bud retorted by pointing out he knew and lived with his mother for six years. When Billy next slanders him for not knowing who his father was, without even thinking about what he was saying, Bud responds, "My daddy plays a giant fiddle and his name is Herman E. Calloway" (p. 94). But after having said the idea aloud, the idea grew "bigger and stronger" in his mind as he wondered exactly why his mother held on to the flyers and began to speculate that she was trying to leave Bud a message. In Bud's mind, his mother felt "too embarrassed about why [his father] wasn't with [them]," so she dared not talk about his father aloud (p. 94). Instead, Bud concludes, that she left him a subtle message through keeping a flyer with the name and picture of his supposed father printed on it. Hence, using the clues concerning the collection of his mother's flyers and her suicide, Bud draws the conclusion that his father's name is printed on the flyer that made her so upset, the name being Herman E. Calloway.