What are those glowing blue shields in Resident Evil 5 for?

They are the BSAA emblems. There are a total of 30 in the game. If you shoot them you can collect stuff such action figures or buy extra costumes in the "extra" menu voice. And there's also the trophy for getting all of them. :)

You can get Sheeva's tribal costume collecting all 30 of them

See here for their location

Grabbing all 30 gets you that lovely getup, plus something special for Chris and a number of other trinkets