Dumbledore gave Harry a pack of cards that had portkey functionality, under the name Santa Claus and claiming that they were a portkey to Salem, but instead heading to a location somewhere in London. Harry gave them back for further investigation, thinking that they might be a trap, Dumbledore took them back but didn't activate the portkey.
It's possible that this was just a short reference, meant to establish Dumbledore's steps of trust in parallel to the gift of the Cloak of Invisibility, and that Harry did not retrieve the portkey and Dumbledore did not place it upon Harry's person...
But activation trigger was to rip the King of Hearts -- a king card known for its face character stabbing itself in the back of the head -- in half.
By the way, who gave the Cloak to Harry?
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 114, and also, as a special case due to the exceptionally close posting times, chapter 115.
There is a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)