I believe the US system is very different - anecdotally I'm told it's one license, i.e. you can get a gliding 'endorsement' on your PPL etc.
Chris Reed and Sedbergh have summed the practical state up nicely. However, I do think it's rather sad for gliding.
While I don't have an arguament with some rating/qualification above standard solo to fly passengers, the instructor rating involves a significant amount of time, is external to the club (requires leave, not done at my convenience), and is targetted at teaching someone. It also means I'm going to get stuck on a rota flying trial lessons: All because I want to take a mate for a flight occasionally. Not really worth the agro.
To contrast, having moved to aus, I got signed off to fly passengers in a day: some pre-reading about passenger handling, a handfull of backseat flights to prove I could fly ok from the other end of the cockpit, some Q&A / passenger awareness, and a signature in my logbook.
I've always thought it's one of the great shames of gliding that I can't share it / introduce friends to the experience.