documentclass{article}
usepackage{calc}
usepackage[bibstyle=authoryear]{biblatex}
addbibresource{jobname.bib}

renewbibmacro*{begentry}{ifkeyword{ownwork}{textasteriskcenteredaddspace}{}}

usepackage{filecontents}
begin{filecontents}{jobname.bib}
@inproceedings{foo,
  author       = {Foo},
  title        = {Foo},
  booktitle    = {Foo},
  year         = {2017},
}
@inproceedings{bar,
  author       = {Bar},
  title        = {Bar},
  booktitle    = {Bar},
  year         = {2017},
  keywords     = {ownwork},
}
end{filecontents}

begin{document}
nocite{foo,bar}
printbibliography
end{document}

renewbibmacro*{begentry}{%
  ifkeyword{ownwork}{%
    setlength{dimen0}{-widthof{textasteriskcenteredaddspace}}%
    hspace{dimen0}textasteriskcenteredaddspace%
  }{}}