At this time RS limits the # of rows that can be in a Signal Output to 1 Million. The information in this article explains how to control the size of your signal.
You can reduce the size of your signal (# of Rows) by adjusting these 3 settings:
# of Rows ~= Geo Grain x (Date Range / Time Granularity)
Two of the easiest ways to reduce the size of your signal include: