I'm an Instructor Trainer/Instructor for Sea Signs. It's one of my favorite (and most popular) classes to teach. Students generally leave the class wanting more.
The class includes about 120 signs that will enable you to actually have logical conversations underwater. It is PERFECT for instructors and divemasters to communicate. The current class focuses (not exclusively) on safety and simple commands/instructions. In speaking with Sea Signs, I know there is a followup course coming out shortly to complement the current course.
Generally, the class is about 3 to 4 hours long, includes an informative book (ebook) and DVD video. Most instructors charge around $100 for the class (depending on the instructor that could include materials or not).
When you become a Sea Signs Instructor, the trainer will send you an outline. You can then fill out a Distinctive Specialty application (for PADI) and become a Specialty Instructor for "Safety Signing Diver". If you advertise it as a PADI course, you must issue a PADI certification to ALL people in the class. I do NOT advertise it as a PADI course, however for those who interested in using this course to help get them to a certain certification level, I will send in the PIC for an extra $20 (to cover my cost of the PIC application). Believe it or not, about 80% of my students wish to be certified by PADI, in addition to Sea Signs.
Once a diver completes the user course, they will be registered as a Sea Signs certified diver. Sea Signs will send them a "BC Tag" that will identify them to other divers. There are about 300 instructors and about 3-4000 divers using the system. It has picked up a lot of popularity because of Sea Signs involvement in DEMA.
One of the posts said they would pay money to just hang out and talk diving. This course has that same sort of feel to it. Like I said, it is just plain fun. Lots of stories and lots of laughing.
The biggest issue is there are not a lot of instructors around. If you are interested, PM me and I will send you more information and try and introduce you to an instructor in your area.
http://www.seasigns.com
Hope this helps, jcf