To cite GeneExpressionSignature in publications use:

  Li, Fei, Yang Cao, Lu Han, Xiuliang Cui, Dafei Xie, Shengqi Wang, and
  Xiaochen Bo. GeneExpressionSignature: an R package for discovering
  functional connections using gene expression signatures. Omics: a
  journal of integrative biology 2013 17 (2): 116-118.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {GeneExpressionSignature: an R package for discovering functional connections using gene expression signatures},
    author = {Fei Li and Yang Cao and Lu Han and Xiuliang Cui and Dafei Xie and Shengqi Wang and Xiaochen Bo},
    journal = {OMICS: A Journal of Integrative Biology},
    year = {2013},
    volume = {17},
    number = {2},
    pages = {116-118},
    pmid = {23374109},
    doi = {10.1089/omi.2012.0087},
  }