When they used to have charcoal pellets in the metal can portion, they printed "This end up" on that end. But they switched to treated water repellent filter material some years back and it's no longer marked? Maybe it doesn't matter now, but I still put them in with the can up!! As a primary filter they still work very good. Secondary filters never have anything in them.
Careful . . .I Have a Generator and I'm not afraid to use it !