It means you have an older version of source code pro, the Rust website uses your local font instead of an invalid font name like some websites do.
Re:Why I’m dropping Rust
by MaulingMonkey on Sunday September 11, 2016 @02:40PM
(#12474877)
Happens here too (on Chrome 52-53.) I guess it isn't some locally corrupted font, eh?
Edit: Doesn't occur on IE 11, so it seems Chrome specific.
https://i.imgur.com/Bg8rejM.png