There is no character encoded for use as a pause symbol, though various characters or combinations of characters may look more or less like a pause symbol, depending on font.
In a discussion in the public Unicode mailing list in 2005, a suggestion was made to use two copies of the U+275A HEAVY VERTICAL BAR character: ??. But the adequacy of the result depends on font; for example, the glyph might have been designed so that the bars are too much apart. – The list discussion explains why a pause symbol had not been encoded, and this has not changed.
Thus, the best option is to use an image. If you need to use the symbol in text, it is best to create it in a suitably large size (say 60 by 60 pixels) and scale it down to text size with CSS (e.g., setting height: 0.8em on the img element).