Longman Dictionary of Contemporary English
Wiktionary
n. (context British English) A police identification card, sometimes accompanied by a badge.
Wikipedia
A warrant card is proof of identification and authority carried by police officers and some other law enforcement officers including Immigration Officers. The term is normally used only within the United Kingdom and in current and former Commonwealth countries. Many other countries refer to their equivalent of warrant cards simply as police credentials, commission books, or identification cards. In the UK MI5 officers also have warrant cards.
Warrant cards generally include a photograph of the holder, as well as the holder's name, rank, warrant number and a holographic emblem to mark authenticity. The warrant number is equivalent to a badge number in other police services; it is a unique identifier unlike a collar number (sometimes displayed on the uniform) which may change when transferring between departments or changing rank. A warrant card is sometimes displayed alongside a badge showing the service to which the officer belongs, but is increasingly commonly displayed on one ID card, with the force crest printed on it.
The language on a warrant card usually indicates that the holder is granted authority by a specific official to perform the functions of the office held, and may also indicate training to a particular level. In the UK Police personnel authorized to carry firearms may have an endorsement on their warrant card to that effect.
Usage examples of "warrant card".
She narrowed her eyes, then tilted her head slightly, indicating the warrant card he still held in one hand.
Rebus showed his warrant card, but the guard was adamant, and directed him to the visitors' parking.
John Walker was a large, square-bodied man so obviously a policeman he rarely had to produce a warrant card for identification.
A brand-new, clean warrant card proclaimed him to be Detective Constable Barnard.
He pressed his warrant card to the glass door, and she let him in.