I've never seen such an aggressive and hostile copyright notice in a forum signature before. It's not entirely clear that you can even claim copyright over trivial online comments.
It's not entirely clear that you can even claim copyright over trivial online comments.
Trivial or not, you have copyright in your own writings, online or off-line. Each participant on HN owns the copyright in the written expression of his or her comments. Similarly, a photographer has copyright in photographs taken by that photographer. See a user profile of a high-karma HN participant
for an example of asserting copyright in HN comments, something that any of us could do, because the copyright is already there under modern copyright law, and asserting the copyright openly and publicly helps battle infringement.
A work must be creative enough to earn copyright. Most tweets would not qualify, for example. You can assert anything you want without it being legally enforceable.
There is the complication that photographs of 2D works of art intended to represent the original are not subject to copyright, so some of those photos might not be either if someone with enough money wanted to press the issue. (Not a lawyer)
There's a history of buzzfeed and other link-farm sites writing inflammatory posts based on TMC forum posts. Many posters don't want their content stolen that way, so they put on those notices.
