The NPS and other resource agencies take their protection role pretty seriously. I am sure they are pursuing this as we speak. And yes, they do work through the United States Attorney's office, who represents govt agencies in court. In my experience, I was in court with the US Attorney's Office on several occasions and was amazed at how quickly and professionally their attorneys learned and presented the agency's cases.
Let's be clear. Such vandalism is a clear violation of 36 CFR (code of Federal regulation). The LEOs (Law Enforcement Officers) at the impacted parks will work with the US Attorney's Office to build a case, issue violation citations and/or bring charges - if they determine a case can be made and there is a good chance of successful prosecution.
Signing petitions and writing letters may help some individuals feel better, but will likely have little influence on prosecution. And that is really how it should be. The evidence and the intent determines the case, not how many people who have no direct evidence feel that someone is guilty.
About Petitions: (just my opinion based on experience) Talking directly to a local official will many times (but certainly not always) get more prompt action. I have received many petitions through the years about various projects and actions. My experience has been this, either sitting down and having an honest face to face conversation with the local deciding officer, or writing a heartfelt and rational letter to the local deciding officer is FAR more effective than signing a petition or printing off a form letter from some web page. Those essentially get treated as a form letter, expressing a single thought, albeit one shared by however many people signed the petition or sent in the form letter. Agency decisions are made based on many factors, and public comment certainly plays a role, but agency decisions are not made based on a voting process of how many people are for or against an action.