While many poker rooms offer a reload bonus, Party Poker has special bonuses for existing players. Last month the players of this poker room received codes for various bonuses. In the same month, Party Poker introduced a monthly bonus for the individual player.
So, some players receive re-deposit codes - 20% to 100$. Others are offered to earn a certain amount of points (credited for cash games, participation in paid tournaments) in order to receive a cash bonus.
In order to find out what exactly is available for you, you need to go to the "bonus / promotion" menu item.