Is there a Doctor Who equivalent of the Bat-signal?

I'd like to send said signal out.

PhD student in the lab has never seen any Doctor Who. Colleague is wrongly telling her to only watch the new ones. I am trying to counterweight this with some old school recommendations so what episodes would you recommend for each Doctor?

Edit - I should add that somehow, the only episode she has seen part of is part of the Twin Dilemma.