You can't rely on seeing constructions to indicate claims as some constructions blend into the terrain or are beneath the surface. So until an in game system is implemented I can see the value of a forum based approach.
Sticky a claim thread on the first post have a link to a screen shot or the Google map with the full usable map area revealed and manually update claim zones on to it. Inform all current players on the server and all future players that this thread is the most vital thread in existence for the TOG Minecraftian world.
Don't hide it make it visible and make it current - take a look at the Independence Community Map Project thread from different game as an example ~ Community Map Project v2.0 ~ On Hold.
Its a sticky on the forum - it was manually drawn from exploration and is updated manually as the areas are settled and roads are built etc. Whenever a player has a doubt about their location or areas nearby they look at that map.
We could do something along these lines - the basic idea - use the map to find places to explore, check the map before making a claim or using the land and finally get your claim added to the map. If everyone knows where to look and follows the process there's some 'protection' from 'accidents' and hurt feelings.