The Coke Rewards Rewards site seems to be down due to an expired certificate. The issue hasn't been resolved in at least that past 12 hours. I've run the Symantec SSL toolkit on the domain and as expected it reports the same error as Safari. The certificate expired on 2015-Jan-17 17:16:16 GMT.
This is not the first time I've noticed a large corporation failing to keep it's SSL certificates in check. Last year, Oracle's Support website experienced a similar issue.
The interesting thing with the Coke Rewards site is the expired certificate breaks the website from rendering properly as resources are accessed over SSL.
Here's what the site looks like now:
The issue seems to extend further with the .com domain showing a 404 error:
This is what the Symantec SSL toolkit reports about the domain:
Given this issue happened after hours and over the weekend, I'd expect the website to be back up and running properly on Monday, however this, to me at least, seems like an issue that should not have happened in the first place.