We've had numerous licence discussions flamewars and instances of violations such as the recent Argh EE gpl thread that was locked.
However this thread is not about any specific violation. This thread is about handling violations.
If
I am a content maintainer and I notice my licence is being violated
Contact the violator via private message, asking for the violation to be corrected by any means possible, failing which the content in violation be removed from distribution. Do so calmly and politely.
If possible state how the violation can be remedied, and why there is a violation to begin with.
My private message was ignored/met with a flame/the violator refuses to comply
Contact moderators of the forums and file sites where the content is being distributed and start a thread showing your polite request and the reply. Do not be aggressive, and do not let your thread devolve into a flame war.
The violator is trying to push through a technicality which would mean an endless discussion resulting in a legal limbo
In this case you are the licensee, and whatever the interpretation, there is cause for doubt on the legality of the content, which should be remedied. An endless discussion will not fix the problem unless either party hires a flotilla of lawyers and goes to court.
If
I am a 3rd Party and notice a licence violation
Contact the licensee privately, explaining how you found the violation, where to find it, and who is in violation. Provide as much information as possible.
You may also want to contact the violator and give warning, but it is not your responsibility to handle the violation. It is not your content to defend and thus by going beyond the act of reporting you are going beyond your mandate, when it is none of your business.
I messaged the violator warnings that they may be violating another content makers licence, and they're now flaming me/accusing me of causing trouble/trolling me
Contact a moderator.
Content Licenses, violations, and the correct way
Moderator: Moderators
Re: Content Licenses, violations, and the correct way
IOW, http://www.gnu.org/licenses/gpl-violation.html 
(at least 80% of it applies to other licenses too)
(at least 80% of it applies to other licenses too)
Re: Content Licenses, violations, and the correct way
Some people need the big bold text and formatting or theyll run away at first glance.