Prince Charles wearing two poppies on his lapel during a visit to Canada. The Canadian Mounted Policeman has one on his hat.
There is also the famous poem (we had to memorize this poem when I was in grade school) about WWI:
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.
We are the Dead. Short days ago
We lived, felt dawn, saw sunset glow,
Loved and were loved, and now we lie
In Flanders fields.
Take up our quarrel with the foe:
To you from failing hands we throw
The torch; be yours to hold it high.
If ye break faith with us who die
We shall not sleep, though poppies grow
In Flanders fields.
Flanders Fields is also the name of the American WWI Cemetery in France / Belgium:
Flanders Fields is the generic name of the World War I battlefields in the medieval County of Flanders. At the time of World War I, the county no longer existed but corresponded approximately to the Belgian provinces East Flanders and West Flanders and the French Nord-Pas-de-Calais region. The name is particularly associated with the battles of Ypres, Passchendaele, and the Somme. For most of the war, the front line ran continuously from south of Zeebrugge, Belgium, to the Swiss border with France