What does the (1) indicate on the top right next to account name?

SSIA

It's your forum level (that will change to a 2 once you write another post)

To expand on what principal said, it's like a kind of experience bar and it goes up as you post in the general discussion forum/subforums on the site. Trade related posts in the marketplace/price check area don't count towards it.

It just goes up linearly based on your post count, and there's a few sub-levels within a level (the White progress bar). On a previous forum I ran for WoW Classic it was harder to level later on similar to the game Kept it simpler here on d2io just going from forum level 1-99 at the same rate.

I think the post count required for level 99 is something like 600 posts... haven't checked in ages as it was one of the first things I modified phpBB with.

Thank you