MarsEdit supports the system-level panels for entering emoji and special characters that work across all Mac apps. There’s no dedicated menu or toolbar item for this, because macOS already has a great built-in interface.

The Character Viewer

To browse the full set of available emoji and symbols, select Edit > Emoji & Symbols from the menu bar. This opens the macOS Character Viewer, a large panel where you can search for and insert any emoji, symbol, or special character.

Inline Emoji Suggestions

For a more streamlined process, type a word that describes the emoji you want, for example “heart” or “smile”, and invoke Edit > Emoji & Symbols. Instead of opening the full panel, macOS displays an inline popup with matching emoji right where you’re writing. Pick the one you want to insert it.

This can be done even faster by using a keyboard shortcut. After typing the search word, press Control–Command–Space, or use Globe–E if your keyboard has a Globe key. The applicable shortcut is shown in the menu item.

Beyond Emoji

Many other characters, including math symbols, accented letters, arrows, and more, are available in the full Character Viewer panel. You can search within a variety of categories or type a search term that is likely to match what you’re looking for.