[shakna]

HN helpfully uses the referrer, so you can easily do it with a tiny bit of JS:

    <script>
    if(document.referrer == "https://news.ycombinator.com/") {
        // Mess with HN users here...
    }
    </script>

[vidarh]

View source on the linked website just now:

    <!-- DO HN STUFF HERE
    <script>
        if(document.referrer == "https://news.ycombinator.com/") {
             window.location = 'https://bbenchoff.github.io/images/Brogrammers.png'
        }
    </script>
    -->