Superman only finds out that his mother kept a scrapbook of his exploits when it was stolen by Lex Luthor's henchmen. The scrapbook goes missing for a while before mysteriously reappearing on Kent's desk. Even Batman is unable to determine who stole it - or more importantly why.
The existence of the scrapbook, and its connection to the Kent name, threaten to undermine Superman's secret identity.
The scrapbook supports the hypothesis of Amanda McCoy - namely that Superman is Clark Kent. The ramifications of McCoy and her obsession ultimately culminate in her confronting Superman (Action Comics #653) and later in the events of "Dark Knight Over Metropolis" (beginning with Superman #44)