Website using the £ symbol on their website - meaning it may accept payment in this British currency.
Google+ platform websites integration using the Google+ platform tag.
The Tweet Button is a small widget which allows visitors to share content and connect on Twitter.
Let visitors recommend your content on Google Search and share it on Google+.
Content Security Policy is best used as defense-in-depth, to reduce the harm caused by content injection attacks.
Open graph description entity tag
Open graph title entity tag
Sites who has this tag are verfied by google to use WebMaster tools