Comedies were usually named by the profession or particular quality of the main character, e.g., “The Grouch” or “The Girl from Samos.” Sometimes the name referred to a plot development, “The False Accuser.” (In such cases, the audience knew what to expect; the enjoyment was in the unfolding of the play.)
Mark’s play was not a comedy, but as a whole it was not a tragedy either. The part before the Last Supper is often humorous. The main character does not really have a profession—one could not call the play “The Fisherman” because he is not a fisher of men. So I think it is likely that Mark referred to the play by the name of the main character.
One possibility is that the play was named “Christ,” i.e., “The anointed one.” That name, however, does not give much information to the person who hears of it for the first time. “There’s a play scheduled for next week: “The Anointed One.” How, when, why?” People of various stations in life were anointed for various purposes. The name itself is not particularly entertaining in itself. In any case, if I heard about a play with that name, I would assume that the anointing occurred early in the play, and the rest of the play concerned the consequences of the anointing. But that does not happen in Mark’s play.
So let me try another possibility. Possibly the play was named “Jesus Christ,” i.e., “Jesus, the anointed one.” That name would have told the audience in advance that the protagonist was their divine intermediary, Jesus, and that he would be anointed at some time in the play. They thought of him as their heavenly high priest—an anointed one. This name “Jesus Christ” gives the audience enough information to anticipate the play.
I note that the name “Jesus Christ” would not have ‘given away’ the end of the play, because the audience did not know how Mark would unfold the story. They could expect an anointing to take place during the play, but not how or when. Or if the anointing would be for both Jesus’s role as high priest in the heavens and for his death. So the play name “Jesus Christ” situated the story in their knowledge, yet Mark could extend the story artistically and surprise them.
I note that the only contemporary texts extant that combine “Jesus” and “Christ” are the original versions of the Letter to the Hebrews and the Letters of Paul. It was all too easy for later redactors to backfill mentions of “Jesus” or “Christ” in these texts as “Jesus Christ” to show that the concept of “Jesus Christ” existed in the earliest Christian texts. Contrariwise, if we imagine Mark in a world where the concept of “Jesus the anointed one” was novel (except to the author of the Letter to the Hebrews), the title “Jesus Christ” had real dramatic value for him and for his audience.