Labeling the backs of photos?

[Toecutter]

Any ideas on how best to label my signed photos?
I store mine in archival sleeves in binders.
Looking into the long run, I'd like for folks to know who is in the pic.
I'd like to very lightly write the actor's name on the back of the pic so they can be ID'd.
What type of pen/pencil would be best to avoid bleeding through the paper and not do any damage?