Is it the image of a female empowered Indiana jones? A swashbuckling character that can run on walls? Or a gun that allows you to pick up anything in the game and launch it at anything else? What about a racing game where the whole point is to crash your car as spectacularly as possible? The signature doesn’t even need to be gameplay related. Halo would have played the same if set in a traditional spherical planet, but it would be hard to get as excited about it.

And when it comes to a signature, Midway couldn't have asked for a more timely one than the Low-budget hong kong martial arts film look combined with ridiculous fatalities. Mortal Kombat featured an aesthetic combination that players had strong cultural associations with, was largely underused to this point, and really gave players something to talk about. It was a perfect signature.

It's important to remember that many other games have failed in their attempt to follow nearly identical steps, such as the largely forgotten Way of the Warrior, leading one to believe that an important part of the formula is explicitly not following someone else's formula. It’s not effective as your signature if it’s following someone else’s. In the words of Titan Quest developer Ben Schneider “Don’t copy superficials! Instead, reverse engineer!”

A signature also helps guide your team along their unique path. In this way, the signature is basically the incarnation of the overarching design goal of the game. Everything that will need to flow forth to support that signature will be in support of the overall target as well. Normally this direction can be managed without a specifically designated signature, but in an established genre, it’s essential.

When Shiny decided to make a 3D shooter, they decided to eschew the “bigger guns, bigger explosions” mantra that had driven most titles since Doom. Instead, they decided to focus on making the most elegant weapon possible: the first sniper rifle. This gave the player the ability to zoom across a mile or more of simulated terrain and place a bullet firmly wherever the player wanted.

Every aspect of the game development, from world creation to weapons powerups to technological performance, was directed by this signature change. Not only was this gameplay device so memorable as to drive sales, it has become a staple of all FPS games since. The possibilities of this weapon were a gold mine waiting to be discovered and explored.

3. Leverage players’ expectations of rules to create unique interactions

Generally, games must be constructed in such a way that the players rules and goals are clear and instantly recognizable, but the interaction of those rules are unique. When creating in an established genre, this allows you to rely upon the stereotypes created for that genre. There is an interesting contradiction here. God of War seems instantly familiar to anyone who has played Devil May Cry, Onimusha, or any number of other 3d action adventure titles.

But this 2005 smash combined just about the right level of the traditional and the fantastically original. When dropped into an ancient 3rd person world with some god stomping your hometown and an insane character holding insane swords of doom, the player immediately know what they're supposed to do. But then they added an intense focus on animation via real-time events.

This gave a working framework for the player / character to do any fantastic thing the artists dreamed up. So while they player knew what they could do (basic rules) and what they had to do (basic goal), they never knew quite what was going to happen (interaction between rules). Unique gameplay happens in the space of getting a sense for how rules uniquely interact.