MEMPHIS, Tenn. — When the flags were removed from the caskets and folded with military precision, there were no relatives there to receive them. So, they were passed, hand-to-hand, through the crowd. Some mourners wept as they clutched the flags briefly. Others kissed them. But the three veterans laid to rest on a rainy Memphis morning were strangers to most of those who gathered to honor their memory. The service was part of a national effort by funeral homes, medical examiners, state and federal veterans’ affairs departments, and local veterans’ groups to pay final respects to members of the military whose bodies were not claimed by any relatives.