My DS5 has been a loud-in-public reader since he was two. It's easier now that he's older. Apparently he read outloud 'water evacuation system' printed on the side of a visiting fire truck last fall in preschool. I guess the firefighters got quite a kick out of that. I think my normal response is to smile sheepishly and say, "yep, that's what it says." Rinse and repeat if necessary.