I personally don’t own any, but I remember seeing a signed Cobb (Bat On) at a Chicago area card show in the late ‘80s. I was pretty young at the time and remember being blown away by the sight of a Cobby autograph on a T206. The card was in pretty rough shape, heavily damaged with a large chunk missing from one of the upper corners (top left if I remember correctly). Cobb’s standard green ballpoint pen signature ran across the front at an upward angle.
Not sure if this is the same signed Cobb (Bat On) you already know exists, but thought I’d mention it just in case you don't already know about it.
I would love to see that card again.
Steve