You don't. That's up to the author to provide in the text:
Code:
<p>They read the tavern sign:</p>
<div class="sign"> - Wonky Willies - </div>
<p>With nothing negative to note, they continued inside.</p>
You wouldn't want, or expect, the TTS to say "quote" before reading the sign...it would just read the sign.
An epigraph may, or may not, need a "quote" in front of it. If it doesn't, use a div.
Code:
<div class="epi">
<p>From the Dawn of Time we came</p>
<p>Moving silently down through the centuries</p>
<p>Living many secret lives</p>
<p>Struggling to reach the time of the gathering</p>
<p>When the few who remain will struggle to the last</p>
</div>
<blockquote>
<p>From the Dawn of Time we came</p>
<p>Moving silently down through the centuries</p>
<p>Living many secret lives</p>
<p>Struggling to reach the time of the gathering</p>
<p>When the few who remain will struggle to the last</p>
<p class="sig">~ <cite>Juan Sanches Villa-Lobos</cite></p>
</blockquote>
Offset text is a visual presentation....anything can be offset/styled visually...... If it is not a quote, use a div and css to style the visual offset/color/font/border/background/etc.
If it is a quote of someone external to the narrator (-ish) that you would say "quote" or use airquotes, or in some meaningful way indicate to the reader that it is a quote of another person - and it is a long quote - then use blockquote. If it is a short quote then you can just incorporate that into the flow of the paragraphs (not offset) and use quote symbols and/or the <q> tag.
Code:
<p>A great movie line was said by a young William Wallace in Braveheart (1995):
<q>“They may take our lives, but they’ll never take our freedom!”</q></p>
That would not need the TTS to say "Quote" before reading because it is in the flow of the text.