1. Create a new expression smart field
2. Select the Constituent table as the Target Table
3. On the Criteria tab, enter a string to be placed in the field such as: 'Multiple Gifts on One Day'
4. On the Filter tab, enter:

[BBCM_Constituent].[RERecordID] IN (SELECT CONSTITUENTID
FROM BBCM_GIFTS
GROUP BY CONSTITUENTID, GIFTDATE
HAVING COUNT(GIFTID) >1)

5. Click OK and process the smart field.

note: Actual table and field names may vary based on the data mart