The mural in the central city police department references the Justice League.
Left to right. Green Lantern, Flash, Wonder Woman, Superman, Batman, Green Arrow, and Aquaman.
Coast City, where Barry goes to get the pizzas, is the hometown of Hal Jordan, the Green Lantern. The "Welcome to" billboard says "Home of Ferris Airlines." Hal Jordan worked at Ferris Aircraft as a test pilot. The Flash and Green Lantern are both members of the Justice League.
Hannibal Bates is a play on the names of the infamous characters Hannibal Lecter and Norman Bates.
Paul Blackthorne and Katie Cassidy make guest appearances as their Arrow (2012) characters Quentin Lance and Laurel Lance / Black Canary, respectively.