Read Be careful what you copy: Invisibly inserting usernames into text with Zero-Width Characters by Tom Ross (Medium)
Zero-width characters are invisible, ‘non-printing’ characters that are not displayed by the majority of applications. F​or exam​ple, I’ve ins​erted 10 ze​ro-width spa​ces in​to thi​s sentence, c​an you tel​​l? (Hint: paste the sentence into Diff Checker to see the locations of the characters!). These characters can be used to ‘fingerprint’ text for certain users.

A cool little trick with text for embedded steganography, security, or other communication purposes. 

This could also be used for pseudo-private communication via Webmention even. Just hide your messages inside of public messages.

Aaron Parecki bookmark Be careful what you copy: Invisibly inserting usernames into text with Zero-Width Characters (medium.com) ()

🔖 ❤️ OnlineCrsLady tweeted in his cryptography/blockchain talk for #Domains19 @poritzj mentioned steganography, so I wanted to share with him, plus with anyone interested in such weirdness, the Latin Steganometrographia for creating cryptographic poetry in Latin: cool, bizarre, fun! https://t.co/5JawIqhbQF https://t.co/jqnJPJZcwh

Bookmarked a tweet by Laura GibbsLaura Gibbs (Twitter)

👓 Hiding Information in Plain Text | Spectrum IEEE

Read Hiding Information in Plain Text (IEEE Spectrum: Technology, Engineering, and Science News)
Subtle changes to letter shapes can embed messages
An interesting piece to be sure, but I’ve thought of doing this sort of steganography in the past. In particular, I recall having conversations with Sol Golomb about similar techniques in the past. I’m sure there’s got to be prior art for similar things as well.