Hi Andy,
The small symbol in the lower left corner is a linked sign for the family. This is new function in IV2009.
A family with linked symbol means that this family is copied from another family, its parent family. You can right-click on this family to select Family Properties, then click Link Tab, you will see the information about the link, including Creation method, Parent Family Name and so on.
If family A is copied from family D, then A is linked with its parent family D. If D is changed, for example, adding a column, then A needs to be updated.
Thanks,
Corrine