=216.= If the countersign be lost, or if a member of the guard deserts with it, the commander on the spot will substitute another for it and report the case at once to headquarters. =217.= In addition to the countersign, use may be made of preconcerted signals, such as striking the rifle with the hand or striking the hands together a certain number of times as agreed upon. Such signals may be used only by guards that occupy exposed points. They are used before the countersign is given and must not be communicated to anyone not entitled to know the countersign. Their use is intended to prevent the surprise of a sentinel. In the daytime signals such as raising a cap or a handkerchief in a prearranged manner may be used by sentinels to communicate with the guard or with each other. =Section 12. Guard Patrols.= =218.= A guard patrol consists of one or more men detailed for the performance of some special service connected with guard duty. =219.= If the patrol be required to go beyond the chain of sentinels, the officer or noncommissioned officer in charge will be furnished with the countersign and the outposts and sentinels warned. =220.= If challenged by a sentinel, the patrol is halted by its commander, and the noncommissioned officer accompanying it advances alone and gives the countersign. =Section 13. Watchmen.= =221.= Enlisted men may be detailed as watchmen or as overseers over prisoners, and as such will receive their orders and perform their duties as the commanding officer may direct. =Section 14. Compliments from Guards.= =222.= The compliment from a guard consists in the guard turning out and presenting arms. (See Par. 50.) No compliments will be paid between retreat and reveille except as provided in paragraphs 361 and 362, nor will any person other than those named in paragraph 224 receive the compliment. =223.= Though a guard does not turn out between retreat and reveille as a matter of compliment, it may be turned out for inspection at any time by a person entitled to inspect it.