Cool find from Little Big Details. Apparently the waveform image used in the iOS icon for Voice Memos is the word "Apple."
I love the attention to detail in Apple's icons. See also: Reda Lemeden's visual history of the iTunes icon, the Preview Kid getting removed from his icon, "Here's to the Crazy Ones" being written on the Notes icon, and the iOS Maps icon showing Apple's new campus location, and probably a bunch more that I can't remember right now.