In Reddit, you [link via Markdown](https://en.wikipedia.org/wiki/Markdown). The site renders this its own way, so it can add a "external link" character if needed - and that character is a part of the user interface; a side channel, not a main signal. E.g. copying from a Reddit post, you wouldn't want to find that character in the pasted text.

There's text-based webbrowsers like Lynx too