I used my handheld GPS and Google Earth to make a map. After I planted each bed, I marked it in my GPS as Bed 1, Bed 2, etc. When I finished, I went to Google Earth and had it pull up a map of my area with all the waypoints marked on it. I have a coresponding spreadsheet with information listed for each bed such as date planted, where I purchased the seed, the conditions the seed was planted under, and so on.
I can't speak for the rest of you gentleman, but it would have been just as easy for me to physically mark each plot is some subtle way. If some trespasser was walking through my property, unless they were a total dope, they would have to wonder what was going on when they hit all those cleared out areas in the woods. They stick out like a sore thumb.