Sentence:  This meant , concretely , that the patient could not read at all without making writing like movements of the head or body , became easily confused by `` hasher marks '' inserted between hand-written words and thus confused the <WSD>mark</WSD> for one of the letters , and could recognize a simple straight line or a curved one only by tracing it . 
Meaning of the word marked with <WSD> tags:  a visible indication made on a surface