I've never thought about where to place my fork when I'm done eating. But, over the holidays, my sister came for a visit, so I took her out to a nice restaurant. When we were done with our meal, I had put my fork with the prongs turned down on the plate and its handle on the table. She politely whispered to me to put my fork ON the plate. Is this some kind of etiquette rule?
To indicate to the waiter when you are finished with your meal simply place the fork and knife side-by-side (parallel) on the plate, either horizontally or diagonally (handles at either 3:00 or 4:00). The tines of the fork can be up or down, but generally when eating European style, the tines are down.
Also, as a general rule, while you are eating and resting between bites, the handles of the fork or knife are not supposed to touch the table once used. Place the knife at the top of the plate with the sharp edge facing toward you.