Is There a Special Marking for a Topic?

The topic is the default co-referent in gapping. So we assume that the subject is the same from clause to clause. In topic prominent languages, anything you leave out in subsequent clauses is going to refer to the topic not to the subject. It may make no sense at all to think about the topic as participating in some sort of hairy tree structure that generatives love so much. But movement is easy to talk about when you want to indicate that something will always be first in an utterance.