Hello,
Trade badges were supposed to be worn on the lower left sleeve. Signal Qualification badges,signal blitzes, were worn on the right sleeve centered between the elbow and shoulder unless there was a rank patch worn. It was then worn above the rank patch. The drivers qualification badge was worn on the lower left sleeve. Brian Davis has a great section referring to Heer trade badges in his book GERMAN ARMY UNIFORMS AND INSIGNIA 1933-1945 John Angolia and Adolf Schlicht take it in depth in their book UNIFORMS AND TRADITIONS OF THE GERMAN ARMY 1933-1945.
Here are some examples that I have.
Fred