Was gonna say that yea, TF2 does this to an extreme. Not just silhouette but also movement style, weapons, and voice.
An interesting side effect for some games is that hit boxes (target size) start to vary when you vary the player sizes. What do you do when one character is 2x bigger in area than another in a shooter game? The big one can get hit more - so you need to consider balance such as giving them more health or some other balancing attribute that makes it worth it.
WoW does this well, at least on the racial level. I still don't like the lack of customization overall, but you can certainly tell the different races apart by silhouette.
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