It isn't always immediately obvious how to type special characters such as an interrobang on Facebook messages and updates. The easiest method is to copy and paste the symbol from another webpage. While the interrobang does have its own keyboard shortcut within Windows, this usually won't work within a Web browser.
Log into Facebook and begin typing your update or message until the point where you'd like the interrobang to be inserted. Open up a new browser tab and load a page that displays an interrobang, such as a definition page in an online dictionary.
Click and drag across the interrobang symbol to highlight it. Press "Ctrl+C" to copy the symbol to the Windows clipboard.
Switch back to the tab displaying the Facebook page. Place the cursor where you'd like the interrobang to appear and press "Ctrl+V" to paste it in. Continue typing the rest of your update or message and hit "Enter" or click "Post" or "Send" to publish it.
An interrobang can also be displayed by holding down the "Alt" key and typing "8253" on your keyboard's number pad. This method works in desktop programs (such as Microsoft Word) but does not generally work inside Web browsers because of the different way they handle special characters.
The Merriam-Webster online dictionary defines an interrobang as "a punctuation mark designed for use especially at the end of an exclamatory rhetorical question." You might also want to use the punctuation marks separately ("?!" or "!?") to achieve the same effect.
A variety of other shortcodes can be used to insert other special characters on Facebook. Some of the more common ones -- such as the em dash (Alt+0151) -- will work on Facebook in a browser application.