There are various types of Mahamudra: sutra Mahamudra, tantra Mahamudra, essence Mahamudra (A brief overview [pdf]
). Only the last-mentioned type features "pointing out instructions" which were mentioned above. A skillful teacher might be able to point out the nature of the mind and thus lead the student to a sudden realization of enlightenment. But to receive these instructions, a student normally has to undergo a rigorous preliminary practice (Ngöndro
In one of his dhamma talks, Ajahn Brahm mentioned a profound discussion he had with some tibetan monks. He concluded that the words, the instructions and techniques might be slightly different. The results, however, are the same. To quote him directly: "Same cake, different icing"
There is also an interesting book written by Joseph Goldstein ("One Dharma") which investigates the similarities of buddhism's three main branches (Theravada, Vajrayana, Zen). It's highly recommendable