Green’s Dictionary of Slang

chickee! excl.

also chickie! chicky!
[chicken n. (2a), i.e. one is acting in a cowardly manner]

[1910s+] (US) a warning of the impending approach of authority – whether police officer, parent or teacher – and thus a command to stop whatever one is doing that might cause that authority to act against one (cf. chiggers! excl.).

In phrases

lay chickie (v.) (also lay chic, ...chick, ...chickee, keep chickie, keep chips, stand chickie)

[1930s+] (US) to maintain a lookout (during a crime).

play chickie (v.) (also play chicky)

[1940s+] (US) to maintain a lookout; usu. during a crime.