Marks - A mark refers to anything that was written on the poster - ink, pencil, paint, etc.
While a lot of times the writing is on the back of the movie poster (which might cause bleed-thru), some posters also have doodles or markings made on the front of them in the artwork on the poster.
If the marks are on the border or back of the poster, they generally shouldn't decrease the value of the movie poster. However, if there's bleed-thru, marks on the back of the poster are more likely to decrease the value of a movie poster.
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