Wikipedia says "Enter Ctrl+⇧ Shift+u, then type the four hex digits, and press ↵ Enter.". For that you need to know the unicode code of your symbol, which you can get in gucharmap or on the web. You can just copy symbols from gucharmap (or web) as well, that's what I do when I need funny symbols.
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Is there a way to enter characters like the Celsius symbol for example in medit?
Wikipedia says "Enter Ctrl+⇧ Shift+u, then type the four hex digits, and press ↵ Enter.". For that you need to know the unicode code of your symbol, which you can get in gucharmap or on the web. You can just copy symbols from gucharmap (or web) as well, that's what I do when I need funny symbols.