That's a nice idea but the thing is forum would have to verify that the account over there belongs to you too. If not scammers would have a way to fake the identity of an account on many of those exchanges just to use as an edge to scam people here and that won't be nice.
It's not something the forum itself should be doing to be honest. I was thinking it would be something the user himself would be able to do. But I just don't have any good idea on how to display them.
That way there is no issue about scammers, and anyone who wants to talk to the user on the other platform can just verify with him/her that they have the account ownership.