"Good-by," I said. I stepped out into the rain and the carriage started. Catherine leaned out and I saw her face in the light. She smiled and waved. The carriage went up the street, Catherine pointed in toward the archway. I looked, there were only the two carabinieri and the archway. I realized she meant for me to get in out of the rain. (Book II, Ch. 24)
Just a nice example that demonstrates that non-verbal communication is inferential (not very controversial) and that part of what has to be inferred is illocutionary force (probably more controversial).
If that is too cryptic, consider this question: What does Catherine mean by pointing? What might Frederic have initially thought she meant?