The Bellamy salute, first used when the Pledge was introduced in the 1890s. It consists of extending your arm at an upward angle toward the flag, wrist straight so your palm faces outward and downward. It is the proper way for civilians to salute the American flag, unless one is a Socialist New Dealer.

It's used in other countries. I remember passing a rural school in Mexico in the 1980s and seeing the children gathered around the flagpole saluting the Mexican flag one morning.