Chapter VI : Distinctive emblem - Art. 21.
Art. 21. The distinctive flag of the convention can only be displayed over the sanitary formations and establishments which the convention provides shall be respected, and with the consent of the military authorities. It shall be accompanied by the national flag of the belligerent to whose service the formation or establishment is attached.
Sanitary formations which have fallen into the power of the enemy, however, shall fly no other flag than that of the Red Cross so long as they continue in that situation.