Little green rectangles under your username...

[Starwhip]

I just noticed these. What do they mean and how do you get them?

[astropapi1]

They're reputation points. You can try asking a moderator for more detailed info.

[technicalfool]

If people think your posts are awesome, they can add to your reputation by clicking the little star icon that unfortunately doesn't exist in the Space Lounge or Forum Games. If someone with a high reputation votes you up, you gain more reputation points than if a newbie votes you up.

Basically, as you gain more reputation, your upvotes become worth more.

[razark]

http://forum.kerbalspaceprogram.com/threads/51861-Forum-feature-highlight-the-reputation-system

[fatfluffycat]

they tell you how many cookies you have, so 1 green bar= 1 cookie and so on

[DisarmingBaton5]

http://forum.kerbalspaceprogram.com/threads/51861-Forum-feature-highlight-the-reputation-system

This. You have just applied to the Kerbal Space Program