Medical writers from the UK, USA and Australia have developed a checklist that they hope Journal Editors might ask authors to complete to deter unacknowledged or inappropriate writing assistance (or 'ghostwriting'). It has been published in PLoS Medicine (doi: 10.1371/journal.pmed.1000023) with a debate on ghostwriting from editors and researchers.
I should declare my interest, in that I am one of the authors (and definitely not a ghost)!