Sentence:  [...] Officers must maintain control by making sure their inmate count is correct, by checking inmates' passes as they walk the hall [...] This helps prevent the occasional juggling of goods, gang communication, such as <WSD>kites</WSD> (a written request from one inmate to another), and inmate assaults, such as face cuts or stabbings. 
Meaning of the word marked with <WSD> tags:  A (usually concealed) letter or oral message, especially one passed illegally into, within, or out of a prison.