My colleague used a custom web font where every glyph was replaced with a filled circle. Better browser compatibility, you know.

Although our reason was actually to do with password managers. At $DAYJOB we have a CRM/ERP system with lots of password fields for other entities (not the current cookie user). It's increasingly difficult to opt out of browser autofill, and LastPass in particular was corrupting password data in the system whenever forms were submitted.