In Fortnite Chapter 5 Season 1, you may notice a gold-orange-yellow circle moving across the map. This circle essentially follows a player, in the same way as bounty board circles.
The player following the golden circle has a Association medallion, who polishes their shields. You can eliminate the character holding the medallion and take it for yourself, but keep in mind that this character will be buffed and will be harder to eliminate. The more medallions they have, the more shield improvements they will have, so you should approach the character within the golden circle with caution. (We didn't discover any striking images of the character with the locket, but it's possible we just weren't close enough to notice it.)
Because there are multiple medallions, there can also be multiple gold circles on the map. This remains the same: it is players who have the medallions.
You can use this golden circle as a warning: the player inside is not to be tampered with. You can also target it: the player in the circle has some good loot to grab from.
Otherwise, medallions can be obtained by eliminating boss NPCs in specifically named locations.