Monday, June 14 is Flag Day. The occasion is marked by a public celebration each year at Baltimore’s Ft. McHenry National Monument and Historic Shrine. Here are a few things you might not know about the American flag:

When the flag was adopted by the Continental Congress in 1777, the colors had no specific meaning. But the colors on the Great Seal of the United States, which are the same as those on the flag, do. White symbolizes purity and innocence; red stands for hardiness and valor; blue signifies vigilance, perseverance and justice, and the stars represent, according to a book about the flag published in 1977 by the House of Representatives, “the heavens and the divine goal to which man has aspired from time immemorial.”

President Woodrow Wilson officially proclaimed the anniversary of the Flag Resolution of 1777 on May 30, 1916, and President Harry Truman signed an Act of Congress in 1949, designating June 14 of each year as National Flag Day.

If the flag is flown upside down, it is a distress signal.

The flag should be displayed from sunrise to sunset, but it may be flown 24 hours a day if it is properly lit at night.

The flag should not be allowed to touch the ground when it is raised or lowered. It should be raised briskly and lowered ceremoniously.

It should be saluted when it is raised or lowered. Those in uniform should give the appropriate military salute, and civilians should place their right hands over their hearts. Men wearing hats should uncover and hold their hats over their hearts.

The term, “Old Glory,” was invented by Captain William Driver, a shipmaster from Salem, Mass. in 1831.

The flag may be cleaned and mended when necessary, but if it is too worn to be flown, it should be destroyed by burning in a dignified manner.

No flag should be placed above the Stars and Stripes.

When the flag is displayed against a wall, the union, or field of stars, should be at the top, to the viewer’s left.

When it is displayed on a speaker’s platform, the flag should be placed above and behind the speaker.

The flag should be flown at half-staff for 30 days from the death of a president or former presidents. 10 days from the day of the death of a vice president, the chief justice or retired chief justice of the United States or the speaker of the House of Representatives.

To signify mourning, the flag should be hoisted to the peak of the staff for an instant before lowering it to half staff.

If the flag is placed on a casket, the union should be positioned at the head and over the left shoulder. It should not be lowered into the grave or allowed to touch the ground.