and signing message will not cut it, because some of those were not carrying any address in their profile
A message posted in their profile is useless as there's no logs of them and anyone can change it on a whim. They need to be on an unedited post on the forum from a long time ago so people can prove they account belongs to them without a doubt.
You're right. That's what this thread is for -
I guess there's still the risk of the person quoting it being an alt but it's better than nothing.