The frame-builder Ed Litton has been working on my bike, and he found a Falck mark stamped into the tubes. He told me Falck tubing was often used for the more budget-bikes in a lineup. However, Falck also made high quality tubes too, so it's not an absolute indicator.
Litton also said the owner (I forget the name) of the Falck factory was assassinated by Italian communists
My frame is double butted tubing for a Mexican-made Windsor from ???? year.