To cite 'ggsignif' in publications use:

  Ahlmann-Eltze, C., & Patil, I. (2021). ggsignif: R Package for
  Displaying Significance Brackets for 'ggplot2'. PsyArxiv.
  doi:10.31234/osf.io/7awm6

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{ggsignif}: R Package for Displaying Significance Brackets for {'ggplot2'}},
    author = {Ahlmann-Eltze Constantin and Indrajeet Patil},
    year = {2021},
    journal = {PsyArxiv},
    url = {https://psyarxiv.com/7awm6},
    doi = {10.31234/osf.io/7awm6},
  }