25B6; BLACK RIGHT-POINTING TRIANGLE
The fonts on my system that have this symbol are:
Kozuka Mincho Pro
Lucida Sans Unicode *
All except one are Adobe OpenType PostScript fonts.
Browsers will usually replace missing symbols on a character (firefox) or paragraph element (opera) basis from all installed fonts. I think Opera holds configuration for Unicode Character Ranges somehwere and uses that. Firefox can switch fonts on literally every symbol. If you have a webpage with normal text and one Japanese symbol, that one symbol might get pulled from another font, not excplitly declared on the webpage. The remainder of the paragraph after this symbol might be shown using that foreign font as well.
I don't know if WinNT 6.1 also does this. But WinXP most certainly does not. I imagine looking up every character into a table of replacements is a very slow process. Especially since Unicode is quite bloated with funny symbols. The symbol only shows up on the Windows title bar if I choose a font which has this 25B6 in it.
You can copy-paste this character into common Unicode capable software like Microsoft Word and browse your list of fonts to see which one has it.▶
Edited by j7n, Today, 12:14 AM.