Naturally, any dimensions provided below the reference line apply to the joint on the arrow side, while dimensions written above the reference line apply to the joint on the other side. In the image above, welds are indicated for both sides of the joint.
Sometimes, a series of separate welds are specified, rather than a single long weld. This is common when thin or heat-sensitive metals are welded on, or where the joint is a really long one. In the following symbol and drawing, 3-inch intermittent fillet welds are specified:
Notice that the weld symbols on either side of the reference line above are offset, rather than mirroring each other. This means the welds should be located at staggered spots on either side of the joint, as depicted in the drawing on the right.
A weld symbol may also specify an angle, root opening or root face dimension. This is common when the base metal to be welded on is thicker than 1/4 inch. The following example is a symbol and drawing calling for a V-groove joint: