I kind of do both.
In the top, left corner on the back of the print I put a code for me to know how I made that print in case I ever have to duplicate it.
It goes something like this:
6/27/2010 R2 X18 ƒ8@24 C2.5 KRST1:20@3
I file my negs by date and roll number. The X-number is the frame number on the edge of the film. I think you can figure out the rest.
I also have adhesive logo stickers that I print up with my name and contact information on them.
My logo is my avatar picture.
I put the logo sticker on the upper, right corner of the back of the print then I sign and date the sticker (with the date the print was made) so that my signature is half way off the bottom of the sticker. In other words, half of my signature is on the sticker and half is on the back of the print. That way, if somebody tries to remove the sticker, they have to remove part of my signature too.
If the print is titled or if I want to make a dedication, I write that directly on the print.
For instance, I reprinted an old photo I took of my brother's dog and gave it to him for Christmas. I wrote the dog's name and the date the picture was taken but I also wrote "Christmas, 2009."
If you are a photographer or if you are just good at figuring things out, you'll probably understand my code. Otherwise, it's gobledygook. But, basically, it amounts to a serial number that I can use to tell one print from another and, if necessary, I can reproduce the print with that information.