RegStatus is your account’s Registration (privacy) Status.

In the Privacy tab under Preferences (on AIM), within the “Allow users who know my e-mail address to find…” panel are 3 radio buttons.

[RegStatus 3] My screen name
[RegStatus 2] Only that I have an account
[RegStatus 1] Nothing about me

…having a RegStatus of 3 just means that others would be able to look up your ScreenName providing they knew your e-mail address.