Best practice is to document the message ids used within the java classes. We've been using class javadoc like this in a lot of places:
/**
* This module is using message IDs in the ranges 14600-14899 and 13400-13499.
*
* This file is using the subsets 14630-14899 and 13450-13499 for non-logger messages.
*
* See <a href="http://community.jboss.org/docs/DOC-16810">http://community.jboss.org/docs/DOC-16810</a> for the full
* list of currently reserved JBAS message id blocks.
*
*/
I've found it's helpful to also leave a comment at the end of the file indicating the last valid number for the file so people are less likely to overflow when they add a message. This is particularly useful if the valid range for the file is small and ends on an unusual number.