I think the sign up Bonus for Bravado has to do with the "poker points" you earn while playing.
So you take the points you earn, and apply them to this table:
The bonus you can be as much as %100 of your first deposit. For example, in an ideal world, if you deposit $150, then you could earn up to $300 in bonuses. You just need to make 1500pts to get that bonus.
I think that's all correct -- the websites can clarify further
It's figured out by how much money you pay to a "ring game" rake -- which I'm pretty sure are their regular cash games.
You also get 3 points for every dollar you spend on entering tournaments.