It would be textarea, placed just below and editable just like the char name textarea on character page. In this area each other character could write a description of that char. Ex. performed functions, physical apperance and any others things he would like to remember. This text would be displayed only on the character page.
In my opinion, very important argument for this idea is quite easy implementation. I mean, adding one more textarea, acting like existing one (char name) isn't very difficult, is it?

Title edited to describe the contents more precisely. -SekoETC