TexDon1,
Does the shop need to lay a fillet weld down, when symbol don't call for it ? Not unless it's shown on the design drawing. (If your company is responsible for desining the connections, you may want to research further).... along the lines of what hogan has mentioned.
If a fillet is needed, how is size known ? The size will be determined by the Engineer of Record and it should be shown on the design drawing.
Basically, if the joint requires more than one type of weld, a symbol shall be used to specify each weld.