In Chrome (though I may have seen similar behavior in other browsers), type in http://www.google.com. You will always be redirected to https://www.google.com. Usually when I do this, I get the good old green lock in the upper left indicating everything is secure. But SOMETIMES I get the the grey lock with the little yellow warning that indicates when you click on it, "However, this page contains other resources which are not secure." It seems to go in runs where I get the good green icon for a while and then I'll get stuck with the grey lock for a while. This behavior is not specific to one website. For instance, bankofamerica.com does the same thing. Does anyone have any idea why this happens?
P.S. It's not simply the standard references to non-https links in the source because using the developer tools all requests are shown to be https except for the initial, redirected request.
Best Answer
It is nothing to worry about most of the time. Many of the web services and applications on the Internet in these days, are not 100% self sufficient and a web page, in today's Internet, is nothing but a combination of many different items from different locations. In order words, because the web is getting closer and closer to be an inseparable part of our social lives, it needs to incorporate many social items as well. Doing so, requires a website to try and retrieve data from different sources, which not all of them are using SSL protocol. This causes that green lock to go gray.
In a simpler language, when a webpage, which is using HTTPS(SSL), tries to incorporate or use some other items (Pictures, scripts, xml or css files, etc.) on other websites or servers, that do not use https, your green lock turns gray. Most of the time there is nothing to worry about, firstly because there is nothing much you can do, and secondly because this usually happens on non-so-highly-sensitive web pages, and you should only worry when it happens on you PayPal or bank account page.