Memorial Day (formerly known as Decoration Day) originated after the American civil war, to commemorate the union and confederate soldiers who were killed .. by the 20th century, Memorial Day had been extended to honor all Americans who have died while serving in the military service .. it typically marks the start of the summer vacation season .. sticker shows the Tomb of the Unknowns (also known as the Tomb of the Unknown Soldier) located in Arlington National Cemetery, which is a monument dedicated to American service members who have died without their remains being identified ..