I would imagine just have a thread specifically for fakes something like:
Brief description: 1905 Half Crown
Picture:
Info about fake e.g. where you saw it, do you own one, how can you tell its a fake, distinguishing features, if it was on ebay did it sell etc.
Saw it on: Ebay, it sold for £225.00
Distinguishing features: It is a bloody awful copy that looks nothing like the real thing! (obviously more detail in a real post etc)
Leave the thread open so people can post pics and info, one coin/info per post and any post not specifically listing a new fake that get made are just deleted so that the thread is purely pictures with information in every post. I don't know what tools you guys have behind the scenes but I can imagine as long as people know the thread is purely for a picture reference and that there is another associated thread for discussion where they can link pics from the 'picture thread' for want of a better description if they actively want to discuss certain features.