This is an container item gained during the Love is in the Air event. When you give a Love Token to a non-guard NPC from one of the major cities of your faction (excluding Exodar and Silvermoon), you gain this and the [Adored] debuff. You cannot gain another Pledge of Adoration until the Adoration debuff ends. You gain this by giving a [Love Token] to an non-guard NPC while you do not have the Adoration debuff.
This pledge also includes other items that you can find more about on the Love is in the Air page.
A guard NPC will give a [Pledge of Adoration] which is mostly different only in name.
There are technically 6 separate types of these pledge containers, depending on the city and faction: