This article describes how to go from a standard table...
...to a table which indicates any columns below a specific sample size with an asterisk and adds a note in the footer:
1. Select your table.
2. In the toolbar go to Automate > Browse Online Library > Modify Footers > Add Column Header Footnote Indicating Small Sample Sizes.
3. Set the Minimum Column n that will be used as the threshold.
4. Press OK.