This article describes how to go from a standard table...
...to a table that indicates any columns below a specific sample size with an asterisk and adds a note in the footer:
A table with rows and columns.
1. Select your table.
2. Go to Properties > RULES on the object inspector.
3. To apply the rule, select the Plus (+) > Modify Footers > Add Column Header Footnote Indicating Small Sample Sizes.
4. Set the Minimum Column Sample that will be used as the threshold.
5. Press OK.