I would firstly like to say that the Trophies is amazing in xenForo. It is so much fun and really get's the community together and add's extra fun and adventure to every forum.
When a user wins the Trophy a box on the page is displayed with the info (You won,etc).
So you have the page on the forum. And a small "box" displays a medal image with the Trophy name and saying you won it.
I have seen this on some website's and it works great.
http://www.wowhead.com/ <-- When a user wins a trophy it displays it on the page.