In this thread on the T-Mobile forums there are a few people talking about water damage indicators. The OP mentions this:
When I remove the back of the phone and the screen is face-down on a table, the triangle is just above the left side of the micro SD card door. It's visible even with the battery left in place.
...which another person confirms is a water damage indicator.
If you don't see any pink triangles I think you're in good shape.
Edit: Does your phone look like this with the battery out? Because it looks to me like that white circle near the bottom right is the only water sensor on the body of the phone itself.