Marks are earned by passing tests.
The Mark of the Guildsman is reserved for those who pass the Trial of the Guildsman. You must be above level 35 to qualify for this test. To receive the Mark of the Guildsman go to the Town of Giran and meet Warehouse Keeper Valkon.
The Mark of Prosperity is reserved for those who pass the Test of Prosperity. You must be above level 37 to qualify for the test. To take the Test of Prosperity, go to the Town of Giran and meet Warehouse Keeper Parman.
Mark of the Maestro is reserved for those who pass the Test of the Maestro. You must be above level 39 to qualify for this test. To take it, visit First Elder Lockirin of the Dwarven Village.