Digital BW, The Print

Normally, I mark the back of framed prints on the outer layer--the backing board or foam core.

Now I have a special situation which really needs a "do not reproduce," etc. right on the back of the print because it is a celebrity.

Sharpie is out!!  My first thought is using a micro-point (.1mm or so) gel pen lightly.  Any thoughts if this will bleed? 

I don't trust acid-free pre-stick labels at all over the long term.

My only other thought is to try to use the mulberry paper and rice starch for a label.  Same as used for archival hinging.

Does anyone have another tried and proven technique?

Thank you,

Seth