Who is using welding symbols to to communicate the detailed information necessary for welders to complete the weld?

An engineer or a craftsperson

Explanation:

Welding symbols allow the engineer or draftsperson to communicate detailed information about the weld to the welder. In most cases, the welding symbol has an arrow, which points to the location on the drawing where a weld is required. The arrow is attached to a leader line that intersects with a horizontal reference line. The arrow and leader line point to the joint in question, while the weld symbol tells the welder what type of weld   to do. If the weld symbol is below the reference line, the weld should be made on the same side as the arrow.