Winter's Brunt Hammer Skin
From Guild Wars 2 Wiki
“Double-click to consume.
Seasonal. For sale only during the Wintersday season. Use anytime to upgrade the appearance of a hammer. Usable only by hammer wielders.
— In-game description
All Wintersday wooden weapons have a wintery snowflake glow as well as a pulsing white branch design. The hammer's branch design creeps around the hammer's head. A picture of the hammer's glow can be seen here.