What does the "in" icon mean?

[Jimmy]

I'm aware of Facebook, Twitter, and Google Plus as the meanings of the other icons, but I don't know what the icon that says "in" means.
Go to any question at answers.yahoo.com and you'll see 4 icons on the lower right of the box that has the question; they are Facebook, Twitter, the "in" icon, and Google Plus

[JanetM]

This is a good example of why some questions don't receive answers. What "In" icon????! You didn't say. You said something about being aware and named 3 social networking sites... but not what you're aware of, or why you mention those sites at all. Nothing here makes any sense. If I could figure out where there's an "In" icon, I could possible tell you what it mean... other than the opposite of "out". I don't see such an icon anywhere on this site. The only think that seems like la possibility at the moment would be in regard to an InBox in email.

[..ωнιzzz..]

That is for users that have a LinkedIn account which is a social network for work professionals http://mashable.com/category/linkedin/