Now I saw this picture of the Team Fortress 2 classes lined up in silhouette, and I don't know if I feel that they're strikingly different (I mean, they're mostly all middle aged men and very close in height to each other), but you can easily read what role they would probably be. There's the wrench hanging off of the Engineer's belt, Pyro's fuel on the back of his suit, the size of the Heavy compared to the Scout, the ammo and grenades strapped to Soldier... you can clearly tell who the characters are supposed to be (on a side note, I'm trying to figure out if the silhouette on the right is the Demoman or not... he has a collar that covers half of his face, but this lineup might be from an early version of the TF2 characters; the box on his belt tips me off because it could probably be a detonator).
Here's another example of silhouette, but this time from more of a design perspective (and an animation perspective... but of course this could and should be related to gaming as well).
A lot of people have used this example, but it's only because it's a really good example of character design. I'm not too partial to the movie, but each character in Aladdin was created using a certain geometric shape to differentiate them from the other characters. Simple shapes that compose the characters evoke certain qualities about that character. If you gave this sheet to someone and erased the names of the characters from the shapes on the bottom (with the knowledge that these are characters from Aladdin) anyone could guess who they were right away. The simplicity and variety of these shapes makes for a memorable cast of characters.