WOT, also called Web of Trust, is a firefox add-on the recommend to a site. I used it about a year already, and it never fail me at notifying me about the reputation of a website. It's a cumulative data that is voted by WOT users. After you install WOT, you can vote too.
As see at picture beside, google.com.my is a trusted website. It's voted green by users, and the human figures in 5/5. So you can definitely trust it.
I encountered some website that has 5/5 human figures, but the circle is red, just like picture beside. So, I kind of confuse at this part. So, I made my conclusion assume that human figures indicate how many persons has voted for it in a ratio (eg. 3 human figures means 3 millions voting), and the circle colour is average colour that people vote. This is my assumption only, don't believe it 100%, i will update when i got the answer. But, what you can 100% trust when you got green circle and 5/5 human figures.
You can download WOT here for firefox user. For non-firefox usage, you can download WOT at its homepage. It supports all popular browser.