I don't believe that security cameras or huge signs are the way to go. Lets not forget that when Walt built the park that he wanted everyone to forget about the outside world which is why their is a berm around Disneyland. Now if you put in noticeable security cameras all over the place and huge signs its going to remind people about life outside the berm. Did anyone even politely ask the group of teenagers to calm down? Sometimes you would be surprised how nicely they might respond. Even if they don't calm down, just inform a CM and usually they will handle the situation. I have seen it happen many times.