How do you find out if you are a life member of FORG and if not, how do you become one?

If you click on the 'Edit Profile' ink under your avatar (top right of the screen) you will see your membership type. By clicking the Join Us button on the home page you could then go to the PayPal link and pay the $100 dues. Then update your profile.

One presumes Life Members will be so designated by the profiles in the Members List.
To become a Life Member, simply contribute $100 to the FORG cause, and you'll also get (besides the satisfaction!) a neat magnetic FORG pin to display with your other RI pins.