Nitpick: in Catholic dogma purgatory is a place of purification, those in purgatory know that they are there for a reason and only for a certain time, afterwards they enter heaven. Hell on the other hand, is for eternity and ugly. That's why the two are easily distinguished in their iconography, both involve imagery of flames, but souls in purgatory look joyful and those in hell look despondent.
Nitpick: in Catholic dogma purgatory is a place of purification, those in purgatory know that they are there for a reason and only for a certain time, afterwards they enter heaven. Hell on the other hand, is for eternity and ugly. That's why the two are easily distinguished in their iconography, both involve imagery of flames, but souls in purgatory look joyful and those in hell look despondent.