 Businesses specialising in gifts and greeting cards have started merging the respective grandparents days with Mother's Day and Father's Day to try to boost sales.Congress passed the legislation proclaiming the first Sunday after Labor Day as National Grandparents' Day in the U.S. and, on August 3, 1978, then-President Jimmy Carter signed the proclamation.The flower of the U.S. National Grandparents Day is the forget-me-not which blooms in the spring.