The so-called "Dakota access pipeline" is a planned construction project to build an oil pipeline from North Dakota to southern Illinois. Since the spring of 2016, native Americans have organized a protest against this construction project because of its impact on the environment.
In later months, the native American leaders of this protest movement have expressed their disapproval of young white liberals (ie. rich spoiled mid-to-upper class regressive leftist) coming to the protest sites to "support" the movement, taking advantage of the temporary services built there, trashing and polluting the environment with very little regard, and then after a week or so just leaving without cleaning up after themselves, leaving all their trash and waste behind for the natives to clean up.
Which is the sheer irony of what they are doing. They are "protesting" for an environmental cause... by coming to the site, throwing their trash and their excrement around, have absolutely no regards to how they are trashing and polluting the sites, taking advantage of the services provided by the natives, and just leaving without cleaning up after themselves.
This is virtue signaling in its purest form. It makes these rich spoiled regressive leftists feel good about themselves, without actually doing anything useful and, in this case, actually only making things worse, both for the environment and the people who are actually affected by the issue. They pretend to care about the natives, yet their actions indicate the exact opposite. They don't actually care about them, or about the environment, at all; they only care about giving the picture (mostly to themselves) that they do. It's a form of patting oneself in the back for being so virtuous and holier-than-thou.
It is also highly ironic that these are the exact same regressive leftists who say that white people have no place in inserting themselves into the spaces of oppressed minorities. Of course, as the sheer hypocrites they are, they don't have any qualms about breaking their own rules and principles. Because, you know, when you have the moral high ground, everything is permissible and you can do no wrong, and you are free to not follow your own rules which you are imposing onto others. And that's not hypocrisy because, once again, you have the moral high ground and you can do no wrong.