The welding symbol in the illustration is indicating that a fillet weld is required on the arrow side of the joint. The fillet weld is represented by a triangle-shaped symbol placed on the side of the joint where the arrow is pointing. This means that the weld needs to be made on the side of the joint that is indicated by the arrow. The size, length, and other specifications of the fillet weld can be indicated next to or below the welding symbol.
