Here is the first discussion of Fingerprints in Indie Game Design.  This playtest happened before I wrote that post, so the rules took shape as we played. 

I'd just returned from GenCon, brimming with ideas and energy, and went to visit my friend Anat (playtester and artist for Sweet Dreams).  I was describing my Fingerprints setting (superpowers based on whatever you were thinking at the moment of contact with the alien substance), and Anat suggested "counting the holes in the ceiling".  From there it seemed easier to show her than to try to describe it, so we built a character and started playing. 

Anat wrote "counting holes in ceiling" in the middle of her page.  I explained that each player would then get to free associate off of that, and wrote "Understanding your environment" branching from "counting".  She wrote "Leopard Pattern" off of "spots".

Then we talked about what kind of mutation those phrases suggested.  Anat decided on a chameleon ability to create spots on the character's skin to blend in with his surroundings.  I explained that we pass the sheet around again, answering the questions "How does it work?" or ""What does it mean?".  I wrote "bends visible light" on the sheet and Anat wrote "blends in unconsciously, concentrate to remain visible".  Around this time, Anat got that her character sheet looked like a fingerprint.

Then we started the map.  Anat chose City as the scale, and we drew her character (16 yr old Chris) in his house.  I asked Anat for something else in town Chris was opposed to or interested in, and we drew Chris' dad in prison.  So Chris' dad had stolen a chunk of Loa Blood and hidden it in the house.  He got arrested, and then Chris accidentally touched the stuff while counting the ceiling tiles. 

Chris' first action was to sneak into prison and visit his dad.  Anat rolled 1d6 for Chris, and 1d6 that I gave her for the prison, rolling directly on Chris' Fingerprint (character sheet).  She got a 3 on "visible light", and a 6 so far into the white space around the pagee that even stepping it down to a 1 couldn't quite reach "unconsciously".

I narrated the 3"visible light" for the prison, saying that enough guards saw chris flickering by that the city now knows someone has a chameleon power, and high security will now include full light spectrum cameras, lasers, and mirrors. 

Anat narrated the 1"unconscious", saying chris noticed a creepy guy in the cell next to her dad.  We wrote "Creep Out" on the map. 

Then we played out the scene with Chris' dad, who revealed that he had stolen the Loa Blood from the docks, and that he was holding it for a Buyer.  We added the Dock and the Buyer to the map. 

Then it was my turn.  Since I didn't have a character, I chose to act as Creep Out, saying he overheard the conversation, and was now using his underworld influence to search for Chris.  This only affected Chris, and Creep Out, so I rolled 1d6 on the map, and got a 6 on "Creep Out".  We decided that Creep Out was the incarcerated head of a global criminal syndicate, and now they were all on the lookout for Chris.

So that's the basics of the mechanics in action.  I'll post more later.