Can anyone tell me what this symbol � is and why it's popping up within text as I'm browsing on the internet

I'm finding this symbol (�, a black diamond with a white question mark inside of it, just in case it doesn't look the same in your browser!) next to letters that may be in special fonts, but also within words that don't have special fonts. I can't pinpoint exactly when it started appearing, but it is definitely within the last 3 weeks or so.