I just thought of two ideas. First of all, when you go to 'Your Pokemon' you can only tell what the pokemon is, what level it is, if it's in your roster or not, and its gender. My ideas are this:
1.) A marking of some sort indicating which ones have nicknames. (Like if you have twenty level 5 Golurks, for example, maybe you nicknamed one to find it easier. But then you lost it somewhere among the other nineteen.)
2.) Another marking of some sort telling you if it's borrowed or not. (I've had problems with this. I'll have like 20 level 5 Golurks that are the same gender, and then someone will loan me one same level, same gender, for training and I'll end up losing it. :/)
So for those reasons, I think there should be markings on them. Rate these ideas?

Completed, thanks for your suggestion. :)