string text = "Sit to float
                \n
                \n
                \n
                \n
                \n
                \n"; //Customize this string with your own message

default {

    state_entry() {

        llSetText(text, <1.0, 1.0, 1.0>, 1.0);
    }

    changed(integer change)
    {
        if (change & CHANGED_LINK)
        {
            key av = llAvatarOnSitTarget();
            if (av) // evaluated as true if key is valid and not NULL_KEY
            {
                llSetText("", <1.0, 1.0, 1.0>, 1.0);

            } else {

                llSetText(text, <1.0, 1.0, 1.0>, 1.0);
            }
        }
    }
}