I was thinking along the lines of "tally marks", so maybe just a few scratches on the wall, 5 for lowest rank, 3x5 for highest rank.
I'm not good at producing graphics at all, so I'll just link a picture to show what I mean, this is most likely copyrighted etc., so I don't suggest we use it, but somebody should take the idea further.
This could be a cool thing to do, and is easy to add up to in the future when more people have higher amounts of good reports. You could award 1 mark per 1000 or something. I doubt too many people are going to have high amounts which would lead to it looking unsightly.