Sylvie showed Tony Alain's very first sobriety medal from 20 years ago, which she keeps because she was so proud of his first year sober. It's in response to Tony saying it's 'ridiculous' for him to feel so attached to Ollie's drawing.
The medal from the evidence envelope need not be that one; it could be a more recent one. But I don't know if Alain is now dead. In 2006 and 2009, he seems to spend a lot of time hanging about the hotel looking shifty and coughing/going off for a smoke when someone says something significant.
I'm convinced Mark is a bad un. If he ISN'T, and the actor thinks he's playing him as a good guy, it's not a very good performance!
Maybe, as others have suggested, he swapped/planted the medal? I don't know why, though.
I vaguely suspect Baptiste; why is he so invested in the case? And surely his addict daughter will turn out to have been significant?
I also thought Vincent's doctor was a rather funny fish. Is she involved in something somehow? And why are we still seeing so much of him? He must either be involved, or he is there as an example of a somewhat sympathetic paedophile who goes against the popular image – not someone who has a twisted enjoyment of what they do, but someone who is 'wired' that way and is tormented by their feelings.
I too hope it's not as inconclusive as Amber!