.hack//SIGN is a 29-episode anime series, animated by studio Bee Train, that makes up one of the four original storylines of the .hack franchise. Twenty-six of these episodes were shown on television, and three additional episodes, Intermezzo, Unison, and GIFT (a parody between SIGN and the .hack games drawn in an abstract, "cartoony" style) are only available on DVD. In Canada, YTV has aired the Intermezzo & Unison bonus episodes. 

The series was initially shown on TV Tokyo between April 3 and September 25, 2002, but has since been adapted for American audiences and shown on Cartoon Network starting February 1, 2003, and has been more recently distributed on DVD by Bandai Entertainment. 

.hack//SIGN follows the story of Tsukasa (?) as he struggles to cope with his inner self, his past, and his inability to log out of the MMORPG The World. The storyline is quite slow and layered—the viewer is quite often fed false information and red herrings, making it quite hard to figure out what is going on until it is finally revealed towards the end of the series. Character development is also extremely critical to the series; there are few flat characters, and each of the important characters goes through great change through the story. .hack//SIGN has been commented to be a 'talky' series, both positively and negatively, for a story set in a video game. This is viewed as both a positive and negative aspect: some viewers cannot stand the slow plot and minimal action, while others call .hack//SIGN one of the greatest animes ever for the exact same reason. This dichotomy has turned .hack//SIGN into a sort of cult anime.