One thing I've found helpful is to tell them about the reg and say something like "I've seen WDFW here recently and they were passing out tickets - if I were you I'd ..." Regardless of whether WDFW was in the area, this approach always gets a pause from the offender and they usually stop what they were doing (or leave). Using this approach does two things - it educates the offender that they are doing something illegal and it usually stops the action. And done this way you look like a guy just trying to warn someone instead of a guy who is harrasing them, which keeps the risk of coming to blows at a minimum.