I thought that they came with a more "standard" unicrown fork like the one below. Not to say that all Fat forks looked like this. I had a late '80s Schwinn with a fork that looked like the "original gangster" fork that was posted.
I don't think I've ever seen a fat with a crown lug like that, but it is certainly possible. There were lots of custom variations, so it isn't necessarily non-stock. It could have even been a customer request.
To answer the original poster's question, I used to see that fork on like a Fat Chance "Kicker" which was kind of a lower end model than the "Fat Chance" which had the box crown fork and some better components.
If I recall, that fork was not made by Fat City, it was an off the rack fork that did come original on the bike, but was also found on mass produced MTBs like StumpJumper Sports (see below)