It seems like the traditional “No Trespassing” signs aren’t as effective as they used to be, so we’re heading back to class to explore alternative colors that could indicate “stay out” or “keep away” more effectively. We often associate red with stop or warning, yellow with caution, and other colors with different meanings. Recently, I discovered that purple is also being used for this purpose. Is this a new development? It’s way cheaper than trying to buy signs that people walk right by anyway.