I am a Long Term Volunteer with CalParks and my assignment is trail maintenance and invasive plant eradication. Over the last 15 months, the number of visitors enjoying the outdoors of the parks has greatly increased. Some of the visitors may have not spent much time hiking in the outdoors/wilderness and seem to have little knowledge of outdoor/wilderness etiquette. They have trouble with closed areas, staying on the designated trail, smoking, litter, and in some cases their own safety. The park I am assigned to does not have a manned gate so there is no one to greet or give them information. Does anyone have any ideas on how to get some basic hiking knowledge out to them?
Sounds like you have typical visitors. A question. Do you war any kind of uniform or shirt, etc. that would indicate to a visitor that you have some sort of official standing? If not, just suck it up, let it go, pick up their trash, and indicate to park admin that things are going downhill.
otherwise you must be very diplomatic and soft-spoken in your reaction, because you appear to be just another dude in the park imposing your opinions on others. You might try getting video and license plate numbers. Take notes to remember details in case you might have to testify. How would you request backup if you see criminal activity or some sort of emergency?
Signage might help to some extent, but what really works is a uniformed presence.
Unfortunately those kinds of people are everywhere. The best thing you could probably do is... if you see something, say something. Besides the outright littering, sometimes people don't know or understand what they are doing is wrong. Such as stepping off the maintained trail. If you see someone doing something like that, it's a perfect opportunity to educate them and let them know why doing stuff like that can be harmful and have negative impact to the environment around them. Then you just hope they have a moment of understanding and learn to do better.
Leave No Trace Signs may help.... sorry to say that putting up signs that say there are hidden cameras for the protection of guest and animals. People are scared of getting caught on camera....