Some wikis have a custom favicon thingy on the left hand side bar, whereas some don't even have one. I'm not talking abt the actual favicons, I'm talking abt the "second favicon" on the left. See the images below:
(ignore the erased information which is a bit personal, see only the arrow)::
That wiki is the Verticality Wiki which has no "second favicon". Now look at the DanTDM wiki:
Now this one has a custom "second favicon" as you can see. The wiki in the first image doesn't, but the wiki in the second one does. Also in fact I think the majority of wikis don't have this second favicon.
What is this new type of favicon anyway, what is it called?? Also, how does one put a custom second favicon on their wiki (or it something automated)??