You might, for example, hand a positioning and messaging document to marcom so that they know the key messages to include in brochures and to highlight in all of their PR efforts. What happens, unfortunately, is that marcom quickly forgets the recommendations and inserts their own content.
Being an effective "messenger for the market" requires you to communicate on a regular basis with your team members. It means one-on-one meetings with members in which you build consensus for your recommendations. It means presentations in which you present and discuss your recommendations instead of just handing people documents.