Plain text for the Bitcoin symbol
Like Murch said, there isn't a current text based symbol for it, but if you're going to use it on a web application, you can always use Font Awesome.

After you include the fontawesome library, you use the bitcoin symbol like this:

&lt;i class="fa fa-btc"&gt;&lt;/i&gt; fa-btc


Example output of the code above would be:



You can find more information regarding fontawesome bitcoin symbol documentation here.