It is randomly generated by Google Ad sense. I am quite older so I get erectile dysfunction and penis enlargement medications ( I kid you not). JaGex does not control the adds that go onto their site, Google does.
It's not an advertisement. Runescape partnered with miniclip a while ago and created a banner for them.
Basically if you click the link from the miniclip website it will take you to runescapes website but a banner will be displayed on top and at the bottom...