Senses
挂号/ 掛號 to register
to register at a hospital or other office to get a place in line; to take a number
挂号/ 掛號 to send by registered mail
to mail an important document via a service where it is registered and tracked by the post office
挂号/ 掛號 to be on the books
(slang) to have one's name recorded by the authorities; to be flagged