#WritersCoffeeClub Apr 1: What's your favorite easter egg in your own work and/or another work of fiction?

I don't place much value on easter eggs relative to command of language, compelling characters, and similar concrete measures of writing, but in general I like brief character mentions or cameos like when #RobertCrais's #ElvisCole waves to his neighbor #MichaelConnelly's #HarryBosch or when #AceAtkins had #Spenser in Los Angeles on a case see Crais's #JoePike jogging.