POW Cards were an accessory produced by Doc's Games/Uncle Morty Productions, presumably for use with their line of tiny role-playing games (Dinky Dungeons being the best-known of these).
Set #2 contains 17 cards with comic-book style speech and thought balloons containing various sayings, both short ("OOF!" and "Get him!") and long ("It's a good thing that building was empty today."). There are also 5 cards with empty balloons and 5 completely blank cards, presumably for the creation of one's own custom cards.
Their exact intended use is currently unknown. The Doc's Games catalog describes them as "quoteable quotes."