How do trinkets work?

I've just started playing the game and am around level 10, and just realized that the bonus perks I got with the game are available through the Social/Mail menu. I see that along with some gear and skins, there are trinkets.

How do trinkets work? Are they decorative items only, or like class mods do they add any skills to your character?

Trinkets are purely cosmetic to your weapons, as the Wiki states:

They offer no additional bonuses to weapons and are purely cosmetic.

They are linked to the weapon slot rather than the weapon, so swapping out weapons from the various slots applies the equipped trinket to the weapon immediately.