What kind of pen/marker should I be looking for to use on a CD-R?

I typed CD-R pen on Walmart.com and nothing relevant shows up. Amazon has some results but the prices are a little high. I'm wondering if there's something in the specs I should be looking for when I shop in the pen dept of a retailer/etailer or if these CD-R-safe pens have an "actual" name ---... show more I typed CD-R pen on Walmart.com and nothing relevant shows up. Amazon has some results but the prices are a little high. I'm wondering if there's something in the specs I should be looking for when I shop in the pen dept of a retailer/etailer or if these CD-R-safe pens have an "actual" name --- much like how a "stove" is not simply called a "food heater"
Update: I realize I can write on a CD-R with a permanent marker. I was concerned about the possibility of damaging the disc since I had heard and maybe even read somewhere that certain kinds of ink can gradually seep into the data portion of the disc and cause damage to it. I don't know how quickly that damage occurs.
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