*Safety Not Guaranteed" is a YTMND series based on a newspaper ad featuring a portrait of a young man sporting a mullet haircut next to an advertisement seeking a time-traveling companion.
The original newspaper advertisement seeking a partner for time traveling was written by John Silveira and published as filler in the September/October 1997 issue of Backwoods Home Magazine. After his publisher, Dave Duffy, asked him for something to help fill up the classifieds page, Silveira wrote up a personal ad seeking a girlfriend and the time travel ad as a joke, using the same P.O. box numbers for both ads. As of October 2010, he had received thousands of responses to the time travel one and only five for his personal ad.
Online, the ad gained notoriety after the first "Safety Not Guaranteed" YTMND site was created by axlbonbach on October 27th, 2005. As of May 2013, it has more than 1.3 million views. The background music is Paul Engemann's "Push It To The Limit"  from the 1983 movie Scarface. It was featured in Volume 8 of the YTMND Soundtrack.
Since its launch on YTMND in October 2005, both the photograph of the man and the text of the ad has been subject to myth and parody on YTMND. As of January 2012, there are over 835 different instances of the Safety Not Guaranteed YTMND series. Some of these include a Sean Connery mashup, the text of the ad being read by Don LaFontaine and a smashup with Legend of Zelda: Ocarina of Time. Many of these YTMNDs feature the time traveler's face photoshopped in to images from different time periods across history.
With the creation of "Safety Not Guaranteed Changes Internet History" on March 8th, 2006, the time traveler himself became a popular icon on YTMND. In this instance, the mullet-wearing man is shown going back in time and replacing YTMND with PTKFGS, an alternate universe joke well-known within the community. It also had its own PTKFGS version, Security Not Ensured.
On February 6th, 2006 YTMND user Bluedemon7 vandalized the Wikipedia page for Safety, adding in quotes from the ad. This sparked a fad of other YTMND users repeatedly vandalizing the entry. The vandalism caused the page to shut down edits from new members and was discussed on the Talk page for the entry through June of that year, with two YTMND pages created from the discussion.
Identity of the Time Traveler
The meme also led to an investigation regarding the identity of the time traveller in January 2006, when YTMND user vex5 claimed to call a number associated with the post office box in the ad:
Vex5 claims that after calling the number of those believed to own the P.O. box, he received very suspicious reactions. When asked about time travel, the person on the other end of the phone allowed a short pause, replied "never call here again" and hung up the phone. Another YTMND user, guano, called the same number, getting the answering machine. He announced that the message asks to "leave a message for Mark, Debra… also, Moses or Caesar!"
Other users tried calling the number and claimed to have heard the same message. Some have even managed to record it. In response to these calls, the answering machine message has been changed to say that this number has nothing to do with "time travel" or "going back in time".
Don LaFontaine Reading
On October 31st, 2007 user Blackadders2 created a YTMND featuring a recording that he was able to get the late famous movie trailer voiceover artist Don LaFontaine to read. On September 2nd, 2008, almost a year later, the reading returned to the top 15 YTMNDs due to LaFontaine's death. Soon afterwards, an update of another Safety site, Hard Safety, was made using the LaFontaine voiceover.
Feature Film Adaptation
In 2011, it was announced that the ad will be adapted into a full feature comedy film titled "Safety Not Guaranteed" starring Aubrey Plaza, Mark Duplass, Jake Johnson and Kristen Bell. Scheduled to be released in 2012, the movie is about two magazine employees who head out on an assignment to interview a guy who placed a classified ad seeking a companion for time travel.
The film premiered in January 2012 at the Sundance Film Festival in Park City, Utah, where it was nominated for a Grand Jury Prize and won the Waldo Salt Screenwriting Award. Critics have overall reviewed the film favorably, calling it an "indie darling" and "crowd-pleasing."
The film was released in June 2012, gaining scores of 92% and 89% on "Rotten Tomatoes and a 7,6/10 on IMDb. Reviews for the film were overall positive, saying it had "strong performances, beguiling charm, and heartfelt story" and calling it "a rare gem rife with one-liners but without the gloss of hipster pretense", "making for a pretty warm and endearing movie".
Search peaked in February 2006 and has been on the upswing since the announcement of the film adaptation, which resulted in an even larger peak in June 2012 when the film adaption was released.
 First Showing – Sundance 2012: Colin Trevorrow's Awesome 'Safety Not Guaranteed'
 Indie Wire | The Playlist (via Wayback Machine)- Sundance Review: 'Safety Not Guaranteed' A Grounded, Genuine, Oddly Effective Charmer