The Call Left a Message

Sometimes, when the Call to Adventure is made, no one is there to pick it up. But, as any Genre Savvy person knows, You Can't Fight Fate, and the call won't take no for an answer. If no one's there to pick up, the call will leave a message that can only be "answered" by the person(s) that it was originally intended for. This also has the added benefit of dispelling any doubt that the character might not really be a hero.

It may be a literal message, or a magical artifact (usually a sword), but regardless of its form, it has the same purpose.

Comic Books

 * The Helmet of Fate tends to be this in The DCU. It will transform the person it was intended for into the hero Doctor Fate. If anyone else dons it, the results are not pretty.

Film

 * In 2001: A Space Odyssey, aliens leave the Monolith behind for humans to discover once they've advanced far enough to travel to the Moon.
 * And in the original novel, they put another one on Saturn (Jupiter in the film and in the novel sequels) for them to make the trip to when they've advanced far enough to do that.

Literature

 * The staff Drum Billet passes on to Esk in the Discworld novel Equal Rites.
 * Harry Potter: Surely the Hogwarts letters that just keep on coming for Harry are an example of this? Throw one away? Another is delivered. Throw that one away? They come by the bucketload. Try to take him away to a remote place? A great big fucking giant comes and breaks down your door, bends your shotgun like a licorice stick and gives your son a pig's tail, THEN gives Harry his letter. At last. If that's not The Call To Adventure refusing to take no for an answer, what is?
 * Another one based on (or blatantly ripped off from depending on your perspective) Arthurian legend, in the Wheel of Time: there is the crystal sword, Callandor, the Sword That is Not a Sword, sealed in the Stone of Tear, which only the true Dragon Reborn can take from its resting place.
 * A literal message is left on October Daye's answering machine in Rosemary and Rue.
 * Villanous example in The Saga of Darren Shan where the Vampaneze have a coffin of fire, that only the true leader of the Vampaneze can sit in without dying horribly.
 * One of the books in the Redwall series delivers the message rather forcefully when a bolt of lightning knocks an heirloom sword from its hiding place on a high weather vane. The weapon comes within a few feet of skewering its intended recipient.
 * In Sword of Truth, . Despite all the other Sisters trying first, it could only be triggered by her.
 * In Robert A. Heinlein's Glory Road, The Call comes to the hero in the form of a newspaper ad, specifically tailored to his interests, directing him to appear at a certain office at a certain time.

Manga and Anime

 * The MacGuffins of Digimon Adventure's second arc, the Crests, only activate once their holder exhibits the trait that they were chosen for.
 * Though they can also force a dark Digivolution if what motivates the user is the abuse of their trait; for example, reckless courage rather than for the sake of protecting others. It happened to Tai when he Flipped Off Cthulhu to force Greymon's evolution.
 * The second season does the same thing with similar artifacts, and the fourth has Spirits.
 * The Clow Book in Cardcaptor Sakura: A strange-looking book, in the basement of the 10-year-old heroine, and of all the people who had handled it previously, she's the only one to unleash the cards.

Myth and Legend

 * Older Than Print: Arthurian legend has more than one of these. Other than the Sword in the Stone, the most notable is the Seat Perlious, which was Galahad's call. No one but the greatest knight could sit in it, and considering the number of enemies Arthur had, no one had either the confidence or pure innocence of purpose to actually take the seat until Galahad got to the court some weeks later.
 * In some version of the legends, one knight did make a drunken vow that he would sit in the Siege Perilous. He regretted it when he sobered up but, rather than break his vow and be dishonoured, he sat in the seat and was incinerated.

Video Games

 * The Legend of Zelda: Ocarina of Time does this twice in quick succession with the Master Sword and the Triforce of Courage.
 * Ocarina of Time manages to invert this, actually: Link accidentally accepts The Call seven years too early, rather than too late, forcing him to be put in stasis until he's actually old enough for it. Too bad Ganondorf was expecting this... This is at least partially based on the Arthurian legend/myth of the Sword in the Stone.
 * In Mass Effect, the Protheans left their warning about the Reapers in beacons. Both Shepard and Saren answered.

Western Animation

 * In Transformers: The Movie, even after.