I would also make a frequency pin and carry it in your flight box. A frequency pin is a 4"x4" piece of wood (usually light ply) that is painted white and has your frequency number on it. It should also have a clothes pin glued to it that acts as an attachment device. Some clubs require you to post a frequency pin when your plane is in the air as an additional visual indication of the frequency you are using. Some clubs have other forms of indicating the usage of a frequency and don't require a pin; however, in those instances I still use my pin as an additional indicator. You can't have too much safety.