title: Is there a "glyph not found" character?
body: <p>Let's assume we have a text that contains a Unicode character that cannot be displayed because our font has no corresponding glyph. Usually, a placeholder is displayed instead, e.g. a rectangular block thingy (see screenshot).</p>
  
  <p>Is there a "glyph not found" character that reliably produces this glyph? I'd like to write something like <code>"If the following text contains &lt;insert character here&gt; then you need another font..."</code> in a UI.</p>
  
  <p>By the way, I am not talking about � (<a href="http://en.wikipedia.org/wiki/U+FFFD" rel="noreferrer">replacement character</a>). This one is displayed when a Unicode character could not be correctly decoded from a data stream. It does not necessarily produce the same glyph:</p>
  
  <p><img src="https://i.stack.imgur.com/zekVj.png" alt="enter image description here"></p>