when indexing Virginia birth records I am seeing "Do" often as the surname...what does it mean?
It means Ditto. So the surname before is the same.
Here is a training article:
How do I index ditto marks?
Article Id: 950
, Published November 14, 2020
If a record has a ditto mark or other sign of repetition, type the corresponding information from the previous record or field. Do not index the word "ditto" or the ditto mark itself. Other signs of repetition may include the abbreviation "Do" or a vertical or horizontal line.
Note: Sometimes you will have to depend on contextual information to determine whether a mark indicates repeated information from an earlier record or field, or whether it means something else, such as that no information was given for that record or field.