My version of Chrome on an iMac (latest 43.0.2357.130 (64-bit)) is showing an SSL warning for well-known sites (Hackernews, GitHub, DigitalOcean):
This site uses a weak security configuration (SHA-1 signatures), so your connection may not be private.
However, when I view to the same sites on my other computer MacBook Pro, same version of Chrome and nearly identical setup, I am not getting this warning. Also, my Chrome extensions are synced to both computers, so it is not a rogue browser extension.
Any other ideas and places to look? I'm thinking it is a problem inside the keychain on my iMac.