In America The Radio Technical Commission for Maritime affairs (RTCM) is the body issuing regulations.
The official website of the RTCM is http://www.rtcm.org/
Relevant documents are:
- RTCM 12100.0 Standard for Cration and Qualification of Application Specific Messages (not published yet)
- RTCM 12301.1 Standard for VHF-FM Digital Small Message Services