On your PS3, go into Account Information in the XMB. From there, find the option called Avatar, which will let you choose from a list of avatars to choose from.
If you were wondering if you could have a custom avatar on these, that is not possible, sorry.
Should give us a option when we dont want to use a avatar.
But to OP, you can also visit the store and purchase avatars for 49 cents each. Way more to choose from and more unique than the system defaults.
PS Store>Games>Avatars>All Avatars.
Above posters have it right. I change mine all the time. It's weird I dunno why. I change my sig constantly too... it's a thing.
Like a stereotypical girl and clothes thing, eh?
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