When you hover over one of them, an advert pops up. Usually, it is one of those spam ads about winning an iPad. They make text hard to read in area. Note that it's not only in content pages, its on Recent Changes and in edit summaries too. Why didn't Wikia tell us about this? It happens on both monoook and oasis.
Also, I'm making this as a blog because I a bug with Wikia means I can't reply to or create any forum threads.
NOTE: This isn't actually Wikia's fault, just a virus on my computer. Apologies for my stupidity :P