At the evening of the day of the GBOCharlie gave her father a friendship bracelet. Although somewhat disturbed by the fact that the bracelet appears to be the same seen in his flashforward, Mark decided to wear it, not to put any further distress onto Charlie. ("No More Good Days")
However, following the death of Sheriff Keegan, and fearing for his marriage, Mark eventually decided to get rid of the bracelet, throwing it into his fireplace. ("White to Play")
The words "friendship bracelet" were also written on one of the post-it notes seen in Mark's flashforward, and recreated by Demetri Noh from Mark's instructions.