The answer is to be found in the forum FAQs.
The administrator may have enabled referrals, which allows you to be credited for any new users you invite to the forum.

You gain referrals by promoting CANNABIS.COM Message Boards - Quality Marijuana and Hemp Information using your unique referral link. The link you should use as your referral link is this:

http://boards.cannabis.com/index.php?referrerid=21739

Each time someone follows this link to CANNABIS.COM Message Boards - Quality Marijuana and Hemp Information and registers as a new member, your referral count will be incremented by one. The number of referrals you have can be viewed in your profile.
I do not know if Ron has enabled referrals or not, though.