The 27 MHz RCRS channels are not officially numbered by the FCC. R/C enthusiasts usually designate them by color, and fly different-colored flags from the antenna to show who is on which channel. On the other hand, some CB operators illegally use these channels for voice communications, and usually refer to them as an alternate of the closest voice channel below them (such as 3A, as shown in the table). In CB radios whose channel selector was a multiple-gang rotary switch that presented a binary number to the tuning electronics, it was a common illegal modification to add a toggle switch (or rewire an existing switch, such as the "PA" switch that coupled the microphone to an outside speaker) to modify the low-order bit and thus gain access to the R/C channels.