Author, poet, actress and champion of civil rights, Dr. Maya Angelou (1928-2014) was one of the most dynamic voices in 20th-century American literature. The book “I Know Why the Caged Bird Sings,” an autobiographical account of her childhood, gained wide acclaim for its vivid depiction of African-American life in the South.

The stamp showcases artist Ross Rossin’s 2013 portrait of Dr. Angelou. The oil-on-canvas painting is part of the Smithsonian National Portrait Gallery’s collection.

The stamp features a quotation that the late poet and memoirist didn’t write. The line, “A bird doesn’t sing because it has an answer, it sings because it has a song,” has been widely attributed to Angelou. And ,it is something she might have written, perhaps as a shorthand explanation for the title of her most famous book.  But the line, in a slightly different form, was originally published in a poetry collection from 1967 called “A Cup of Sun,” by Joan Walsh Anglund.

The practice of misattribution has a long history, but it has thrived in recent years thanks to the Internet, where minor falsehoods metastasize at an alarming speed. The scourge of false quotations has even produced a counter-industry of investigative sites and finger-wagging skeptics dedicated to setting the record straight.

But, in the battle between historical accuracy and every single clever observation ever uttered being credited to either Mark Twain or Winston Churchill, the misattributors are winning. In the case of Angelou, who became associated with the quote largely thanks to quotation-aggregation sites and through social sharing online, the misattribution made the leap from the Web and to the world stage.

When Angelou died,  the line about birds that she didn’t write became one of the most common ways that people chose to mourn her online—with many homemade digital memorials featuring the quotation alongside Angelou’s famous, smiling face.