RandomQueue.png
A notification like this is displayed when a friend or guild mate joins a "regular" queue, as in LFG / LFR queue or a Random Battleground queue.
LFGListGroup.png
A notification like this is displayed when a friend or guild mate creates a premade group.
WorldBossGroup.png
A notification like this is displayed when a friend or guild mate creates or joines a queue in the premade group finder tool. The group's activity, name and comment are displayed in the notification.