Users can tell the feature is on if they see "https" in the browser instead of the standard "http." The change helps to prevent an outside party from snooping on a user's searches. For now, the change seems to apply only to the United States home page, and not other sites, like the German or Japanese versions.
It's not clear when exactly the feature was rolled out, but Marketing Land suspects it might have happened around January 8, the date by which Yahoo promised its properties would move to secure servers. It's also not clear which Yahoo properties already have the feature.
We've reached out to Yahoo, and will update this post if we hear back.
Another difference between Yahoo's secure search and Google's, Marketing Land points out, is that Yahoo will stop providing referral information to Web sites with nonsecure servers -- which will make most marketers think there was a plunge in traffic that came from Yahoo.
As with most tech companies post-Edward Snowden disclosures, security has been a top priority. Yahoo in particular has been reeling from a recent attack. Earlier this month, it was discovered that some users in Europe -- and a small number of users outside the region --via the Yahoo ad network.