I see the usefulness of this idea. There have been times when looking through a bargain bin or melt bucket when I thought I saw a better date but couldn't remember if it was the 99o, 99s, or 99(p) that was the good one for example.
I was actually thinking of getting my most valuable coin tattooed a while ago, but there's no way to get it even close to detailed enough. Maybe the cert #, grade, and barcode would be interesting though. There's nothing wrong with a tatt as long as you love it and know that you will forever. It doesn't matter what others think.
RJR Collections is a nice app for iPhone. For coins, stamps, etc. You can even lock it with a password, upload it to a database, and use your own photos.