Source:
https://scmp.com/magazines/hk-magazine/article/2038035/copy-plate HK Magazine
Copy Plate
吹水 (chui sui), v. Cantonese slang. To chat, bullshit.
“Issue a traffic ticket” / “Get a girl’s number.”
Originally meant when a policeman fined you by writing down your license plate; has also come to mean a guy asking a girl for her number.