The Firefly palying cards are a quasi "in-Universe" tribute to the TV series Firefly and the movie Serenity.
 
The pack has no specific character portraits but the fans of the TV show will be delighted to find iconic things like pre- and post-war browncoats for kings, a companion taking a sponge bath for a queen and guns for jacks.
 
Then they're loaded up with little bits and pieces on the cards; notes, stains, stickers from the 'Verse, etc.
 
They're "quasi in-universe" because things like Jayne's hat as the joker or Kaylee's parasol for the red queens are pretty specific.