(1) The emblem must be shown on the flags and the armlets (_brassards_) as well as on all the material belonging to the medical service, but the emblem cannot be recognised unless it is used with the permission of the competent military authority (article 19). (2) Medical units and establishments must hoist the red cross flag accompanied by the national flag of the belligerent concerned (article 21), but medical units which have fallen into the hands of the enemy must not, so long as they are in that situation, fly any other flag than that of the red cross. The medical units belonging to neutral countries which have, in accordance with article 11, been admitted to afford their services, must fly, along with the red cross flag, the national flag of the belligerent to whose army they are attached (article 22). (3) All the personnel must, according to article 20, wear, fixed to the left arm, an armlet (_brassard_) with a red cross on a white ground, delivered and stamped by the competent military authority and accompanied by a certificate of identity in the case of persons who are attached to the medical service and armies without wearing the military uniform. (4) The employment of the red cross on a white ground and the words "Red Cross" or "Geneva Cross" must not, according to article 23, be used, either in time of peace or in time of war, except to indicate the protected medical units, establishments, personnel, and material. [Footnote 251: See below, § 207.] [Sidenote: Treatment of the Dead.]