I don't sign anything. But maybe if that letter didn't sound so much like demands I might consider it.
The company is being asked to give something it owns to the public domain, so demanding that "These items should be made available free to Amigans worldwide. " is not going to work.
As P-J said, it only takes a minute to do, and this is also part of the problem. If it doesn't take any effort to say or do something, then where's the value?
If every person went to the bother of actually WRITING a letter and posting it to Amiga Inc they might take a bit more notice. But this means actually doing something, and from personal experience I'd say that of the 200+ names on that list only maybe 10% would bother.
In case you think I'm being negative for the sake of it, you're wrong. I worked within the corporate environment (oil industry) and these people are ALL THE SAME. They have no empathy, and will only be swayed by possible negative effects to their business.
If you got the backing of some media there might be a chance, but until then I wouldn't hold my breath.