We've had a few questions lately as to what exactly many of the icons/labels you see on your post mean. Here's a key and a bit of information about each item. [Updated May 5, 2013]
This is the name you registered under and will appear to all users.
This is your member title. The only users who have unique member titles are staff members. All other member titles are based on post count. For a breakdown of how post counts affect member titles, see this FAQ topic.
This is your chosen avatar. Controls for avatars are located in "My Settings", which you can access by clicking your username at the top right hand side of your screen. In your profile settings, you will find an option to "Change your photo". You may upload a file from your computer or use a direct link from an image-hosting service like Photobucket or Tinypic. You can visit The Dark Arts forum to request an avatar from a graphic artist.
This is your member group. For most members, their group will be defined by how many posts they have made. A breakdown of how post counts affect member groups can be found in this FAQ topic. Staff members and prefects are placed into separate member groups.
Staff and prefects also have banners relevant to their specific roles displayed in this section.
This is your active post count. Only posts made in areas of the forums which contribute to member post counts will be displayed underneath your avatar.
Your warning points. Failing to comply with the forum rules will result in a warning from staff. You may also be assigned warning points in additional to the written warning. By clicking on "[however many] warning points" you can find out which staff member warned you, on what day, and what rule you failed to follow. Repeated warnings can result in suspension and banning. For more information on these, please visit the forum rules and FAQ section. Your warning points are visible only to you and HPFF staff members. General users can not see what your level is.
Warning points are decreased at the staff's discretion when you consistently help around the forums. Do not contact staff asking for your warning points to be decreased.
In the interests of protecting members, the option to select and display your gender is currently disabled.
This area displays your House banner. You can take the HPFF Sorting Quiz here and PM a Prefect for your Common Room password. If you choose to sort yourself as a Muggle, you will instead have a grey bar that says "Muggle" in this section.
The date you joined the forums.