Half a dozen free-range chickens were scratching on a narrow patch of grass at a farm in Potomac Monday afternoon, looking for insects, seeds and other things to eat. The chickens, with names like Sophia Loren and Marilyn Monroe, seemed happily oblivious to the four cloth chicken dolls stuffed into a cage on the grass before them. But for the humans gathered at Rosie’s Farm Sanctuary, the visual made for a stark tableau.