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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_signatures_with_results(vcs):
 """Returns the list of signatures for which test results are saved. Args: vcs (easyci.vcs.base.Vcs) Returns: List[str] """

    results_dir = os.path.join(vcs.private_dir(), 'results')
    if not os.path.exists(results_dir):
        return []
    rel_paths = os.listdir(results_dir)
    return [p for p in rel_paths if os.path.isdir(os.path.join(results_dir, p))]