As others stated, you cannot advertise your ICO on bitcointalk "normal" ads/banners.

However, you still can advertise your ICO in Bitcointalk users' signatures and/or avatars. A list of such campaigns is here, you can learn from those.
Basically you need funds, best would be to keep them at a reputable escrow, you need a campaign manager and the actual graphics bbcode (for which there are also people here who can help you for a fee).