Arrows represent (somewhat) heavy selling/buying. Heavy selling is usually a sign of institutional involvement. Majority of arrows are buying arrows, and with the volumes usually heavier than those of the selling arrows.
My prediction for next week is that we go up. That said, the beginning of the week (especially Monday) might bring SPY down.
Observe how the beginning of this week was range bound, and sideways. A sign of accumulation, that corresponds with the majority of the red arrows (selling) for the week, followed by an increase in price.