Yes, Magmar's right; the number of Pokeballs under your name increases as you reach certain post amounts. Unless it's changed without me noticing, you get another Pokeball at each of these post amounts: 250, 500, 1000, 2500, 5000, and 10000. However, staff members (forum moderators, global moderators, and administrators) each have a title under their name instead, regardless of how many posts they have.

Oh, and this would probably be better placed in the SMF Help subforum (within "The Binary District"). Questions and comments about this forum itself usually go there. Just wanted to let you know.