All the icons for the threads are either orange or grey with a padlock; except for the threads I have replied to which are an envelope with a green and white arrow.
Edit: That means I have read the post?
I am getting confused now as there are at least two different orange icons with different padlocks.
Green Circle with an Arrow means you are subscribed to that thread (and will receive notifications via My Sitepoint or Email).
As for the padlocks, those are to indicate a closed/locked thread (meaning it isn’t open for discussion anymore).
This is what I have on the general discussion section:
So virtualy every thread is locked!
Hmm… I definitely don’t see that. Interesting… I obviously still have the old icons. @HAWK ; Seems there is an issue with the new icons.
Looks OK to me now.
Jude updated the icons yesterday with new ones to fit our theme, but it looks as if he’s missed some (ie there isn’t a new icon for a thread with a new reply). I’ve just flicked him an email.
Yes there must be something still missing as I am getting a grey icon with a padlock on some threads still.
why i don’t have these icones?
Because they have been updated. Nobody has those icons anymore.
Because the icons have since been updated. 
You can find the current icons at the foot of any forum index page.