Vector flag of an unknown military unit of the Abraham Lincoln Brigade <a rel="nofollow" class="external text" href="http://www.flaginstitute.org/pdfs/Sebastia%20Herreros.pdf">The International Brigades in the Spanish War 1936-1939: Flags and Symbols, fig. 36</a> The white band had some illegible writing.
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Own work based on: <a href="//commons.wikimedia.org/wiki/File:Abraham_Lincoln_Brigade-unknown_flag.png" title="File:Abraham Lincoln Brigade-unknown flag.png">Abraham Lincoln Brigade-unknown flag.png</a>  and <a href="//commons.wikimedia.org/wiki/File:Flag_of_the_United_States_(1912-1959).svg" title="File:Flag of the United States (1912-1959).svg">Flag of the United States (1912-1959).svg</a>