Communist symbolism represents a variety of themes, including revolution, the proletariat, peasantry, agriculture, or international solidarity. Communist states, parties and movements use these symbols to advance and create solidarity within their cause.
These symbols often appear in yellow and red. The flag of the Soviet Union incorporated a yellow-outlined red star and a yellow hammer and sickle on red. The flags of Vietnam, China, North Korea, Angola, and Mozambique would all incorporate similar symbolism under communist rule.
The hammer and sickle have become the pan-communist symbol, appearing on the flags of most communist parties around the world. However, the flag of the Workers' Party of Korea includes a hammer representing industrial workers, a hoe representing agricultural workers, and a brush (traditional writing-implement) representing the intelligentsia.
The hammer and sickle were first used during the Russian Revolution of 1917 but did not become the official symbol of the Russian Soviet Federated Socialist Republic until 1924. Since the Russian Revolution, the hammer and sickle have come to represent various communist parties and socialist states.
The five-pointed red star is a symbol of communism as well as broader socialism in general. The red star was a revolutionary symbol after the October Revolution and following civil war in Russia. It was widely used by anti-fascist resistance parties and underground organizations in Europe leading up to and during the Second World War. During the war, the red star was prominently used as a symbol of the Workers' and Peasants' Red Army from the Soviet Union, which liberated its country from the invading forces of Nazi Germany and went on to rid the rest of Eastern Europe from the fascist occupation forces, achieving absolute victory and ending the war at the Battle of Berlin. Most states in the Eastern Bloc incorporated the red star into state symbols to signify their socialist nature.
While there is no known original allegory behind the red star beyond being a universal political symbol, in the Soviet Union, the red star gained a more precise symbolism as representing the Communist Party, and its position on the flag over the united hammer and sickle symbolised the party leading the Soviet working class in the building of communism. Today the red star is used by many socialist and communist parties and organizations across the world.
The red flag is often seen in combination with other communist symbols and party names. The flag is used at various communist and socialist rallies like May Day, or used in a red bloc. The flag, being a symbol of socialism itself, is also commonly associated with non-communist variants of socialism.
The red flag has had multiple meanings in history but it was first used as a flag of defiance. The red flag gained its modern association with communism in the 1871 French Revolution. After the October Revolution, the Soviet government adopted the red flag with a superimposed hammer and sickle as its national flag. Since the October Revolution, various socialist states and movements have used the red flag.
The red and black flag has been a symbol of general communist movements, usually anarchist. The flag was used as the symbol of the Anarcho-syndicalists during the Spanish Civil War. The black represents anarchism and the red represents leftist ideals. Over time the flag spilled into statist leftist movements, these movements include the Sandinistas and the 26th of July Movement, where the flags colors are not divided diagonally but horizontally. As in the case of the Sandinistas they adopted the flag due to the movement's Anarchist roots.
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The Internationale is an anthem of the socialist movement. It is one of the most universally recognized songs in the world and has been translated into nearly every spoken language. Its original French refrain is C'est la lutte finale / Groupons-nous et demain / L'Internationale / Sera le genre humain (English: This is the final struggle / Let's group together and tomorrow / The International / Will be the human race). It is often sung with a raised fist salute.
The song has been used by communists all over the world since it was composed in the 19th Century and adopted as the official anthem of the Second International. It later became the anthem of Soviet Russia in 1918 and of the USSR in 1922. It was superseded as the Union anthem in 1944 with the adoption of the State Anthem of the Soviet Union, which places more emphasis on patriotism. The song was also sung in defiance to self-proclaimed socialist governments, such as in the German Democratic Republic in 1989 prior to reunification as well as in the People's Republic of China during the Tienanmen Square protests of the same year.
Although not an exclusively Communist symbol, this is a symbol of Irish Socialism. It may have the same roots as the original Hammer and Plough that was replaced by the Hammer and Sickle in Russia. The significance of the banner was that a free Workers Republic of Ireland would control its own destiny from the plough to the stars and the sword forged into the plough would mean the redundancy of war with the establishment of a Socialist International. The flag depicts the Big Dipper, part of the constellation of Ursa Major that is known as "The Plough" in Ireland and Great Britain. The Plough is one of the most prominent features of the night sky over Ireland throughout the year.
In China, the Plough flag (Chinese: 犁头旗), a red flag with white or yellow plough, is widely used in the period of the First Revolutionary Civil War/ the Nationalist Revolution as the flag of the Chinese peasant associations, an organization lead by the Communist Party of China. 
It is believed that Peng Pai (Chinese: 彭湃) was the first user in 1923, at the peasants' association of Hailufeng. The Plough flag has many different versions, some are combined with the flag of Blue Sky, White Sun, Red Field, other are different on the details of the plough. 
Many communist governments purposely diverged from the traditional forms of European heraldry in order to distance themselves from the monarchies that they usually replaced, with actual coats of arms being seen as symbols of the monarchs. In stead, they followed the pattern of the national emblems adopted in the late 1910s and early 1920s in Soviet Russia and the Soviet Union.
"Socialist heraldry", also called "communist heraldry", is a colloquial name for the common design patterns of the national emblems adopted by communist states. Although commonly called coats of arms, most such devices are not actually coats of arms in the traditional heraldic sense, but the recognisable common patterns has led to the use of the unofficial term "socialist heraldry".
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The following graphic elements, while not necessarily communist in nature, are often incorporated into the flags, seals and propaganda of communist countries and movements.
Examples of these symbols in use.
The logo for Antifa