A demonstrator holds a “Black Lives Matter” sign while protesting then-presidential candidate Donald Trump in 2016. The hashtag started five years ago and is an “archetypal” example of a hashtag tied to political issues or causes.

A demonstrator holds a “Black Lives Matter” sign while protesting then-presidential candidate Donald Trump in 2016. The hashtag started five years ago and is an “archetypal” example of a hashtag tied to political issues or causes.