> it would certainly help to show an explicit note that attracts the user’s attention and gives him or her clear instructions about how to act next.<p>Signs do not work.<p>For an examples of signs that don't work look at any large building that has fire doors. These doors (at least, in the UK) are marked with a short, clear, unambiguous, mandatory instruction:<p>"Fire door. Keep closed."<p>The consequences of not following this instruction are, in the very rare occurrence of fire, increased chance of death.<p>But you'll often see these doors left open, sometimes propped or wedged open, or blocked.<p>signs are mostly not useful, and may be harmful. It's probably best to reduce the number of signs people get.