Bruce Almighty illustrates the way that God is ever-present, giving us all kinds of "signs" (literal and otherwise) that clue us in to what's going on around us. Bruce ignored all the signs that crossed his path until his life literally came to a crashing halt. Like most people, he was so distracted by his small expectations for God that he failed to appreciate all the ways God was already interacting with his everyday life.
To his credit, however, at least Bruce acknowledged God's existence... in his own way he asked for God to show up and that's exactly what happened, though this did not work out exactly the way Bruce expected. Thus, Bruce Almighty is a realistic demonstration of how God answers prayer: He shows up in praying people's lives in ways that will grab their attention. Our own stubbornness necessitates drastic action from God, especially when we ask for it.
Toward the end of Bruce Almighty we discover that the homeless man holding up the cardboard signs was God all along. This unassuming man shows up a few times to add some much needed explanation during some of Bruce's most confounding situations. Nice touch.