In my experience, clerks tend to circumvent the issue by simply yelling out, to no one in particular, something like "Next in line!" I've also noticed the acqu

In my experience, clerks tend to circumvent the issue by simply yelling out, to no one in particular, something like "Next in line!" I've also noticed the acquired habit in more experienced retail staff, when confronted with a queue of indeterminate order, to say, "I can help the next customer in line" and leaving implementation of the next method as an exercise for the customers themselves. FWIW, I find the best arrangement is a Fry's style mega-queue with boundaries clearly defined by racks of candy, magazines, or other impulse-purchase crap that feeds into multiple registers.