We use the frequency pin method at our field, and there is a set of pins for 2.4 GHz and a club requirement that we use them.  It's a matter of knowing who is there and what radio (frequency) they may be using.  It may not matter all the much for 2.4 GHz but it is mandatory for ALL 50 and 72 MHz though.  We still ask that 2.4 people grab a pin and replace it on the board with their AMA card (that has a club current year sticker on it).

CGr.