2006 Sacagawea dollar error?? on the "6" of the date 0

[Lauren!]

I have a 2006 mint proof set. When I looked at the Sacagawea $1 coin, I saw a possible strike or error on the "6" and to the right of the "6" on the date. To my knowledge this coin has never been taken out of the proof set.

 

[Greenstang]

Really need a close-up of that area but from what I can see, it looks like it was struck through grease or oil.

 

[Lauren!]

[Greenstang]

It is a Struck Through. Nice closeup pictures.