How to get Legendary Sigils in Guild Wars 2

gamepur.com:

If you’re looking to upgrade your Legendary Weapons, there’s little better way to go about it than adding Sigils to them. Sigils, like all other bits of gear in Guild Wars 2, come in a variety of different quality tiers. The higher the tier, the more stats they’ll add to your gear. Sigils are also a great way to add extra benefits to your weapons that can assist your character in battle. Furthermore, Sigils are vital to securing your best build that will help you excel in the middle of battle.

The benefit of using a Legendary Sigil over a Superior Sigil is that they can take on the properties of any other Superior Sigil in the game. You can also remove them from your gear without having to use an Upgrade Extractor, which is only obtainable from Black Lion Trading Post currencies like Gems and Statues. Additionally, you can change the equipped Sigil stats as needed to suit any build you might be running on your character.

Before, it was possible to obtain a Legendary Sigil from a Legendary Mistforged Trunk or a Legendary Trunk, this method of acquisition has since been removed from the game, and the only way to get a Legendary Sigil is through crafting them at the Mystic Forge:

All of the Gift of Recipes can be purchased from Miyani in Lion’s arch for 10 Gold. You’ll have to combine all of these materials in the Mystic Forge to obtain your Legendary Sigil. The Tier 6 Materials that are needed for the crafting can be farmed on different maps, or you can purchase Heavy Crafting Bags from a Laurel Merchant.