default
{
    state_entry()
    {
        // Set a sit target for link 3, so we can use llAvatarOnLinkSitTarget
        // to detect whether an agent sat on it.
        llLinkSitTarget(3, <0, 0, 1>, ZERO_ROTATION);
    }

    changed(integer change)
    {
        if (change & CHANGED_LINK)
        {
            key id = llAvatarOnLinkSitTarget(3); // read who is sitting on prim 3, if anyone
            if (id != llGetOwner() && id != NULL_KEY)
            {
                llUnSit(id);
                llRegionSayTo(id, 0, "This seat is reserved for the owner only!");
            }
        }
    }
}