They are score numbers just like the one in the corner of your profile image. The total number of scores is 100, and the lowest score of your hubs shouldn´t be lower than 65. Still, when you are new it takes some time for your scores to go up. The score depends on a variety of factors - you can read about them in the HELP section (in the right corner of the page). When I publish my new hubs, they usually start with a 48 to 50 score number and they rise in the next two or three days.