https://news.avclub.com/crisis-on-infinite-earths-confirms-watchmen-as-a-part-o-1840373132

Part 3 of the Arrowverse crossover featured a Watchmen Easter egg. "Special thanks to Damon Lindelof (https://twitter.com/mguggenheim/status/1204824429739380736) for making this one happen," tweeted Arrowverse boss Marc Guggenheim. ALSO: Lucifer's Tom Ellis apologizes for "Crisis on Infinite Earths." (https://tvline.com/2019/12/11/lucifer-crisis-on-infinite-earths-cameo-tom-ellis/)