Column on the far left?

I tried searching but cant find an answer. What is the column on the far left? Is it post activity? Locked? I see some have black boxes and ones I create have green. Could this be explained to me? I am searching for a part and dont want to bother people that have sold it.

Thanks.

 

Scroll down to the bottom of the page and all your questions will be answered

 

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^this is exactly what I was looking for. Not a new member,but New News. Should be added to the newbie FAQ or stickies.

Thank you!