This is an officer of the Cardassian Guard serving a shift as a member of the ceremonial Honor Vigil aboard his vessel. When a Cardassian is slain, a member of the Honor Vigil stands guard over the body until his or her remains can be returned to the family for burial. An officer serving on this shift must do so with no breaks of any kind for the duration of their shift.
Members of the Honor Vigil also participate in memorial services held both on and off ship, where they continue their watch over the body. One sings the funeral chant during the memorial service.
This ancient outfit dates back millennia and is the inspiration for the modern Cardassian uniform.