Mark of Thrallmar

The Mark of Thrallmar is a Horde PvP token earned for world PvP in Hellfire Peninsula and Zangarmarsh, akin to Alterac Valley Mark of Honor. For alliance rewards, see the Mark of Honor Hold page.

Source
You can earn marks in two ways:
 * The repeatable PvP quest awards three marks for capturing forts in Hellfire Peninsula.  Note that as of Patch 2.1.0, this quest can only be done once per 24 hours, but now rewards 150 Thrallmar reputation in addition to the three Marks.
 * Delivering a killing blow to players of the opposing faction in the vicinity of Outdoor PVP objectives in either Hellfire Peninsula or Zangarmarsh awards one mark to each member of the killer's group or raid.

Rewards
Marks can be turned in to Battlecryer Blackeye in Thrallmar or the Horde Field Scout in Zabra'jin for a variety of rewards.

Battlecryer Blackeye offers:

The Horde Field Scout offers: