When vocal staves divide to show different lines on separate staves, it is common to show arrows at the end of the system to emphasize the change, and again at the end of the division to show the staves are rejoining.
Arrows at the start and end of divisi passages on vocal staves are known in Dorico Pro as divide arrows. Dorico Pro shows these arrows on vocal staves by default, but you can also hide them on all staves project-wide.