This time around, it was a number of little things - the attention given to time between dream levels, for example. The turn of the van signifying a change in the gravity of the hotel level, and an intentional amount of attention given to that turn of the van.
As much as reality is taken into question with the spinning of the top, Mal offers an interesting possibility that the police and corporations chasing Cobb around (in the real-life level) are just projections attacking the dreamer.
This is one of those movies where you can't just Google a simple answer - you'll have to make the decision for yourself, which I think is one of the fascinating aspects of this movie.
I searched for all the posts I've written about Inception, and a couple have been about the movie directly, and some have simply mentioned the movie. One of those mentions is in a running diary of The Earth Is Not A Cold Dead Place, which I've always seemed to do in the final week of August - previously coinciding with the start of another school year at Stonehill. Interestingly enough, it's almost the last week of August...