It's like a form of grouping for posts I'm sure you mistakenly changed it to exclamation on a default situation it appears as standard and that's the clipboard kinda icon you see on a majority of posts but in this case you may have mistakenly clicked and changed it to exclamation.
There are many others available in the drop down you can check to see for yourself. Normally everyone ought to use it depending on what their post is about for example if it's a question you change the icon from the drop down bar to question mark.
