A same subject marker is a distinction in the verb morphology of a clause that indicates that the subject is identical to the subject of another clause, such as one of the following:
Thompson, Sandra A., and Robert E. Longacre. 1985. "Adverbial clauses." In Shopen 1985c
Longacre, Robert E. 1985. "Sentences as combinations of clauses." In Shopen 1985c