The United States Patent and Trademark Office has proven to be the place to watch for new Zynga titles, in the sense that the company has been busy trademarking names for future games. FishVille was one example from last fall, then PetVille was another, and now Games.com has noticed that the company has trademarked 21 new games on either December 16 or 21 of last month.

The list includes a range of new and old-sounding genres that use words like: hospitals, hotels, zoos, animals, treasures and crime. Straight from the USPTO:

Readers will note that many other games in these genres already exist. In the hospital category, we have Vojo World‘s Medical Mayhem. In the animal/zoo category, we have Rekoo‘s Animal Paradise, RockYou’s more recent Zoo World, and many others. We haven’t seen blockbuster hotel or “frontier” games on social networks yet, but it’s pretty easy to imagine a simulation game that lets you run your own hotel or create a frontier town. We’re also intrigued by the appearance of gambling-related titles like Poker Blitz, Casino Blitz and Casino World — Zynga had a big hit with its Texas HoldEm poker game but it has appeared to be more focused on sim games these days.

Overall, the list of trademarks suggests that Zynga is continuing its strategy of picking promising genres, then making games that are good in their own right but also tap in to Zynga’s massive cross-promotion ability on its other games and its big warchest for advertising.

Company chief executive Mark Pincus laid out his thoughts on this year in an interview with us from late last month. He emphasized that Zynga is going to try to make its games even more social — so you’re having lots of social interactions with friends inside of games, rather than on Facebook or other platforms. He also said that he expects his company’s games to stay focused on the mass market of social gamers, rather than trying to increase complexity for niche hardcore types:

I think there’s a continued trend towards greater simplicity. We learned that lesson this year. While our games are more accessible than hardcore games, nobody realized making them more simple would unlock more users. Nobody would guess that one of most popular categories would be fish swimming around in a bowl. I would be shocked if it didn’t get even more simple.