I have been highlighting ONLY the series on my bills for about a year. A few days ago, I got a hit that said "Good condition except for a small green stain over the series". Well, that "green stain" was supposed to be my green highlighter mark over the series. So here is what I decided to do. I am looking for opinions on it as well. I decided to get one of those new fancy highlighters (the kind that "rolls on" a thin layer of "tape" (they also make white out like this). It is very easy to apply and seems to hold up pretty well. However, would this highlighter "tape" cause any problems for the bill or would it wear off easily in circulation? Has anyone else used this type of highlighter?