Early july - 30th July
Prior to the permanent wordmark the wiki was using a short lived logo looking like:
This was never really seen as the wordmark however was used for some welcomes etc. The wiki wordmark was officially just a blue link.
30th July 2011 - March 3rd 2012
March 3rd 2012 - Present
The wiki also has a fairly basic Monobook logo, however it's not a permanent logo and therefore it is being changed lots, half of which is messed up.