What I hear lots of times from guys is that they insist they have one piece rims because they don't see a lock ring on the face side. Like Grigg says, the back side is where you see the proof. But to the experienced eye, it's easy from the front because the widow maker has a 5° outer lip while a tubeless has a 15° lip. Here's a link to a pic of the 15° design. The pic is a comparison of what are called "Well Weld" versus "Ledge Weld" designs.
http://i286.photobucket.com/albums/ll89/truckdog62563/Wheel%20Profiles/WellWeldvsLedgeWeld.jpg
