Key Years: 1936-1971
Price Range: $50-$1,400 on etsy
Levi's Big E is characterized by the capital letter "E" in the Levi's red tab. This means this particular pair of jeans was manufactured before 1971, making them a possible collector's item. Why is 1936 important? That's the year Levi's started actually putting the red tab on there. So technically, any jeans or garments in that time may be easier to identify because of it.
Of course, the chances of running into some Levi's big "E" gear randomly in a thrift store is pretty slim these days, but not totally impossible. What you can probably expect is to pay a premium for the stuff from a vintage seller. Levi's production has been so vast that they actually have an in-house historian whose job is to document the historical context of their garments.