So you may be wondering whether you should trust someone based on those fancy coins under their name, or perhaps their post count. The short answer is: Do not use these rankings to determine trust!
This post is intended to show you as a future trader how easy it is to get a rank, so that you can be wiser when conducting a trade. As a side note, I always recommend using escrow when possible, especially when you have not previously traded with someone. Always read their posts in their profile to help determine whether they are contributing positively and to attempt to determine trust. Search the forums for more detail and read the other stickies relating to trading discussions and trust.

All the main ranks that can be handed out to normal users are: Brand New, Newbie, Jr. Member, Full Member, Sr. Member, and Hero Member.
Special notes for Newbie status: If a user has been whitelisted manually by forum administration, they will retain Newbie status regardless of their post count, until they have fulfilled a minimum of 4 hours logged in.

In addition to the main rankings, there are also sub-rankings that can be applied, and those are: SCAMMER, Donator, and VIP. Besides the colors, Donators and VIPs get other perks such as access to a secret subforum dedicated to them, and the ability change their usernames whenever they want from within their profiles. SCAMMERs have several restrictions, but are still allowed to post unless they are banned for another reason. SCAMMERs cannot change their profile (including signature, avatar, etc), cannot edit their posts later, and other things.

Finally, staff sub-rankings are as follows: Staff, Moderator, Global Moderator, Administrator, and Founder. Staff members have access to a special "Staff" board where forum moderation is discussed, as well as to the Donator board. Any staff member can whitelist a newbie, just ask!

Rank	Description	Tag
Brand New:	Zero posts, gets 1 gold coin under his name.
Newbie:	Has less than 4 hours of logged in time, and gets 1 gold coin under his name.
Jr. Member:	Between 5 and 100 posts, and gets 2 gold coins under his name.
Full member:	Between 100 and 250 posts, and gets 3 gold coins under his name.
Sr. Member:	Between 250 and 500 posts, and gets 4 gold coins under his name.
Hero Member:	More than 500 posts, gets 5 gold coins under his name.
Sub-Rank	Description	Tag
SCAMMER:	Manually applied by administration, regardless of post count and gets 5 red Xs under his name.
Donator:	Manually applied by administration after 10 BTC donation, and gets 5 gold coins under his name of which the last is half green. 5 coins are shown regardless of post count when user is a Donator.
VIP:	Manually applied by administration after 50 BTC donation, and gets 5 gold coins under his name of which the last is half purple. 5 coins are shown regardless of post count when user is a VIP.
Staff Rank	Description	Tag
Staff:	Shown when moderators (see next point) post outside of the sections that they moderate. Always shows 5 gold coins.
Moderator:	Shown when moderators of specific sections post within those sections. Gets 5 gold coins, of which the last is shown as half faded-out green.
Global Moderator:	Applied to Staff that have moderation privileges in all boards. Gets 5 gold coins, of which the last is half teal colored.
Administrator:	Has all available permissions and can appoint moderators and perform other administrative tasks. Gets 5 gold coins, of which the last is shown half red regardless of post count.
Founder:	Reserved for Satoshi, gets 5 platinum coins under his name.

To become a Donator or a VIP, send a PM to theymos to get a unique donation address.