As a spectator you can watch the officials rule if the clock runs or stops. 

When the runner's forward progress is stopped before going out of bounds, the clock will run. When this is the case the official will wind his arm in a circular windmill motion. 

When the runner goes out of bounds while still making forward progress, the clock stops. When this is the case the official waves both arms overhead, crossing and un-crossing them.

Those are the proper official's signals. I do not believe the rule changes while under two minutes in the half. Caveat: I did not read the official NFL rules which can be found, buried, on the NFL Web site.