Baltimore police are investigating a sign inside a police transport van that tells passengers, "Enjoy your ride, cuz we sure will!", authorities said on Friday.
Six police officers are charged in the death of Freddie Gray, 25, who died in April from severe spinal injuries after being transported in a police wagon.
WBAL-TV reported that a woman sent the station photos she took on Tuesday when van doors were left open near a station.
In a statement, police called the sign "both concerning and unacceptable." Deputy Police Commissioner Dean Palmere has ordered an inspection of all department vehicles and investigations will be launched "when appropriate," the statement said.
An autopsy report leaked to the Baltimore Sun said Gray died from a high-impact injury as a result of not being secured in a transport van. Gray's death sparked rioting and protests on the day of his funeral and heightened a U.S. debate over police brutality.