You can reapply a floor span direction symbol if it has been removed from the structural floor. 
When you place a structural floor, a span direction component is placed in plan view along with the structural floor. Deck span direction is designated by the direction of the filled half-arrows. 
- Click Annotate tab Symbol panel Symbol panel  (Span Direction). (Span Direction).
- (Optional) To place the tag in the center of the structural floor, select Auto place on the Options Bar and click a structural floor to place the direction span. 
- If you did not select Auto place, select a structural floor. 
- Move the cursor to the desired location on the structural floor and click to place the direction span.