A 1972 illustration of hand signals used to communicate between studio and control room when the mic is live.
“A curious aside here, is that some signals in common usage in the United States, such as the familiar “OK,” made by touching the tips of the forefinger and thumb together, with the other three fingers extended upward and the equally familiar “You’re On” signal, made by pointing the forefinger, are considered to be the grossest of insults in other countries. The OK signal should never be given to a Brazilian, nor the single fingered “You’re On” to an Asian.”
Oringel, Robert S. “Chapter 12: Studio/Control Room Communication.” Audio Control Handbook: For Radio and Television Broadcasting. 4th ed. New York: Hastings House, 1972. 141-45. Print.