I have a theory, that maybe Dragon is linked to Nami somehow. Nami has that weird ability to sense weather, and it hasn't really been explored. We know Nami was orphaned in a war. It wouldn't be so far fetched to say something like Dragon and Nami are from a clan of people that can manipulate weather.
All we know about Dragon so far is that he is from Goa Kingdom, Garp is his father(Who shows no sign of weather abilities), his son is Luffy(Who shows no weather abilities), The mother of his child has not been seen, and his mother has not been seen.
What we know about Nami's past is that her village was supposedly attacked by Pirates, the Marines were called in, a very violent battle happened, and Nojiko and Nami were orphaned. Now in the current story, we know Nami can sense weather, when a storm is approaching and such. Now it would not be like Oda to not go into this, as she is the only crew member who has a strange ability not Devil Fruit related, or explained.
We know that the World Government is not afraid to extinguish entire groups of people on something like the assumption they know dangerous knowledge, and people like Akainu will easily kill the innocent in the name of "Justice".
Dragon is a revolutionary. We know he is from a corrupt kingdom, the son of one of the strongest Marines, and contains some strange connection with the weather, as seen in Loguetown and whenever he is seen, it is sitting out in the wind.
Perhaps Nami and Dragon are apart of a clan of people who can manipulate the weather. My theory is that Dragons mother, or wife was one of these people also. The clan must have been divided and largely hunted down by the government.
Dragon was not raised as harshly as Ace and Luffy to be a Marine, and Garp didn't pressure him. During this time, he became aware of the corruption in the kingdom, and either his mother or future wife became aware of his ability and showed him how to use it. A WG official in Goa discovered this, and had either Dragon's mother or wife assassinated.
In both cases this would lead to Dragon rebelling, and leaving, and him splitting off from his father, as he probably would not think the government would do so at such a point in time.
Because of this incident the WG starts searching the rest of East Blue for any others, they discover Nami's parents(And possibly others) are also people who can use this ability, and seek to hunt them, with the excuse they are Pirates. By the time Bellemere began fighting, the fight was violent enough that the people could be seen as Pirates.
Maybe Dragon's tattoo's are symbols from his clan, maybe he met up with them when starting the revolution.