An internal investigation has been launched after images of a sign in a Baltimore police van went viral on social media.

The sign, which is affixed to the inside of the back door, has the following message for those who find themselves placed inside the van: “Enjoy the ride, cuz we sure will!”

The photos were taken by a concerned citizen when the parked van doors were left open.

WBAL-TV reports that police department officials confirmed the sign is real and an internal investigation has been launched.

Baltimore experienced days of protests and unrest this spring over the death of Freddie Gray, who reportedly became unresponsive while being transported in a police van. Six police officers have been charged in that case.

Baltimore City Police released a statement, saying: "The nature and the posting of wording in one of our transport vehicles is both concerning and unacceptable. We have recently become aware of the wording and have begun an internal investigation to determine all the circumstances surrounding its placement and to identify the person or persons responsible for its posting. This is an incident that is being taken very seriously."