This is your reputation score. Scores are on a scale of -25 to 75 and when you join you're placed in the middle.

Based on your performance here on Steemit this number will go up or down according to the upvotes or downvotes that you receive and the Steem power of those who up or down vote.

The more upvotes you get the higher the number goes and the same is true for the opposite.

Generally speaking it's very rare to see spam posts from anyone with a rep score over 60 and very likely that you will see them from a user with a rep score under 10.

Hope this helps & best of luck with your Steemit adventure!