Is it possible to add arrow symbols in ArcGIS Online?

Answer

Yes, as of the December 2017 update to ArcGIS Online, the arrow symbols are available in ArcGIS Online. The arrow symbols are used to show the line directions in road networks, utility networks, or stream flow.

Note:
For single-arrow lines, the placement of arrow is based on the start and end points of each line feature.

Follow the steps provided below to symbolize the lines with arrows:

1. In the ArcGIS Online Contents pane, select the desired layer, and click Change Style.
   
   
    
2. In the Change Style pane, navigate to Select a drawing style > OPTIONS.
   
   
3. Click Symbols to open the Change symbols pane.
   
   
    
4. Select the desired line color, width, and pattern.
5. For Arrow, click the drop-down arrow, and select the desired arrow symbology.
   
   
    
6. Click OK to close the Change symbols pane.
7. In the Change Style pane, click OK and DONE to apply the changes. The lines now have arrows to show the line direction.