Zynga filed 21 trademarks in December, which helped give the company the most out of any social gaming company, according to a review by the site Inside Trademarks (no relation to Inside Network). Here’s more.

Overall, only around 10% of social game developers seek trademarks for game titles and logos; they are typically the most successful developers, with the highest user engagement ratios.

Zynga filed a total of 26 trademarks over the course of the fourth quarter, 2009. The developer has more than all of its rivals combined, or 38% of all social gaming trademarks from large developers, according to Inside Trademarks. Playdom comes in second, at 14%. Combined with Zynga, the two comprise more than 50% of all social gaming trademarks.

It’s not clear if owning trademarks gives companies a clear edge in the market as game mechanics, graphics and other aspects of a game can easily be imitated. While the industry saw a number of intellectual property lawsuits last year, we haven’t heard of anything significant lately. Obtaining trademarks appears to be more of a defensive move at this point.

If you have a hit social game, in other words, you don’t want other developers ripping off the name and trying to trick your users into joining their apps. We’ve seen a number of people introduce FarmVille-themed applications, for example, that promise to let you do things like exchange FarmVille gifts — Zynga has managed to get those applications shut down, it appears. Although the latest ripoff is gaining fast, as we noted earlier today.

[Pie chart and graph via Inside Trademarks.]