Thank you for your question.
If the coin has a residue, PVC etc. it needs to be removed so that NGC can holder it. The graders can not always determine if the coin is improperly cleaned until it is conserved.
If there is nothing on the reverse, it is usually ignored for the purposes of grading, unless there is something very detrimental like a large scratch. As to the writing, it would be near impossible to verify, so it might just get called graffiti.