Much like the CW bar, when V-bars hit, they were so popular that everyone had a version. For the most part, if they come from a big manufacturer (be it Schwinn, Redline, Win, Wald, etc), they should be stamped. If they aren't stamped, they are either very early, or a knock off. If no stamp, look inside the tubing for a seam...if there is no seam, they are a quality chro-moly bar, if there is a seam, they are either knockoffs or a lower level (in the bmx world) manufacturer, like Schwinn.