The snap coupler was an AC patented hitch system that featured a bell shaped coupler under the transmission that "snapped" when you backed the tractor up to the implement when hitching. It also featured two "hands" on lift arms that matched lift points on the implements to raise and lower the implement. It was a handy system, fast and easy to hook up and go without leaving the tractor seat. Unfortunately the 3pt hitch design became the standard and AC had no choice but to follow in the early '60s.
Most WD45s, CAs, D10, D12, D14, D15 and D17 tractors came with the snap coupler hitch from the factory. Late model Bs could be ordered with it, and WDs could be converted. If you are still uncertain what you have, email me and I will give you a link to my webpage which shows some sc stuff.