Dr. Manhattan looks like Triclops from Phantasy Star III (and what the circle on his forehead is)

except Manhattan has the circle thing (hydrogen atom) on his forehead instead of Triclops’s eye on a block on top of his head.

In case anyone’s wondering what the hydrogen atom means, this is what the internet tells me:

Jon gradually becomes a pawn of the United States government, though the means by which his loyalty is secured are never revealed; he is given the code name ‘Doctor Manhattan’, a reference to the Manhattan Project that, it is hoped, will defeat America’s enemies. He is also provided with a costume which he grudgingly accepts, though he refuses to accept the icon design which is provided for him (this being a stylized orbital model of the atom). Instead, Jon chooses as his emblem a representation of a hydrogen atom, whose simplicity he declares to be something that kindles his respect; accordingly, he painlessly burns the mark into his forehead. This preference for material mechanisms marks the beginning of Jon’s declining humanity, which is progressively mirrored by his gradual shedding of the uniform – by the end of the 1970s, he refuses to wear anything at all except for mandatory public appearances.