Pick up a poppy.

From Veterans Affairs Canada:

• During the Napoleonic Wars, the poppy drew attention as the mysterious flower that bloomed over the graves of fallen soldiers.
• In the 20th Century, the poppy again was widely noticed after soils in France and Belgium became rich in lime from rubble during the First World War. The little red flowers flourished around the graves of the war dead as they had 100 years earlier.
• In 1915, Guelph, Ontario native John McCrae, a doctor serving with the Canadian Forces Artillery, recorded this phenomenon in his famous poem In Flanders Fields.

In Flanders Fields the poppies blow
Between the crosses, row on row,
That mark our place; and in the sky
The larks, still bravely singing, fly
Scarce heard amid the guns below.

In the US poppies are handed out for donations by the American Legion Auxiliary.