Here are some better images...I'm not sure if the line (in the middle of the ink) is from the marker used to sign it...or if it was traced? (ie someone traced an autograph with a pen, leaving that line...and then went over it with a marker). What do you guys think?
Although the "Mickey" looks shaky, I lean toward authentic although a sloppy example. He may have been more intoxicated than usual when signing this one.
Hopefully, the Mantle experts on this forum will chime in. I am fairly comfortable with Mantle but certainly would not consider my opinions ironclad.
I think the line you refer to is just part of the sharpie signature.