Apparently there’s no HTML entity for the flat symbol, ♭. In my previous post, I just spelled out B-flat because I thought that was safer; it’s possible not everyone would have the fonts installed to display B♭ correctly.
So how do you display music symbols for flat, sharp, and natural in HTML? You can insert any symbol if you know its Unicode value, though you run the risk that someone viewing the page may not have the necessary fonts installed to view the symbol. Here are the Unicode values for flat, natural, and sharp.
Since the flat sign has Unicode value U+266D, you could enter ♭ into HTML to display that symbol.
The sharp sign raises an interesting question. I’m sure most web pages referring to G-sharp would use the number sign # (U+0023) rather than the sharp sign ♯ (U+266F). And why not? The number sign is conveniently located on a standard keyboard and the sharp sign isn’t. It would be nice if people used sharp symbols rather than number signs. It would make it easier to search on specifically musical terms. But it’s not going to happen.
Update: See this post on font support for Unicode. Most people can see all three symbols, but some, especially Android users, might not see the natural sign.