ANNEX TO THE CONVENTION : Regulations respecting the laws and customs of war on land #Section II : On hostilities #Chapter I : On means of injuring the enemy, sieges, and bombardments - Art. 27.
Art. 27. In sieges and bombardments all necessary steps should be taken to spare as far as possible edifices devoted to religion, art, science, and charity, hospitals, and places where the sick and wounded are collected, provided they are not used at the same time for military purposes.
The besieged should indicate these buildings or places by some particular and visible signs, which should previously be notified to the assailants.