S - Near the beginning, after the 2nd data post, when you head under the large monument thing, look to the left and it will be in a building window.

O - This is in that building you have to anchor up to get to the top. It will be at the top level in one of the windows.

T - This is on the bridge, you will come to the first broken up part, jump down and turn around to see it behind the gate thing.

M - Before you head out of the train tunnel, the M will be on the left side of the catwalk thing at the end of the wall.

R - This is in the building on the right hand side of the final area before the boss. It is on the lower floor, beside some boxes.