Visible crew/equipment: In the first overhead shot of the Autobots entering Chicago, you can see a small black camera cart in front of Bumblebee and Mirage. (01:47:45)
Visible crew/equipment: At the beginning of the parents taking Sam around to interviews. A camera and rig can be seen in the reflection of the driver side door.
Visible crew/equipment: In the flashback scene with Sam and Carly at the White House, the reflector screen is seen in Carly's glasses.
Visible crew/equipment: During Sam's first meeting with Bruce, at one point, there is a reflection in the ornament on the left side of the desk that shows a large black mass moving in the same direction as the shot is moving.
Visible crew/equipment: In the shot of Optimus driving along with the Driller, part of a camera mount can be seen in the reflection of Optimus' chrome grille. It's definitely not something next to the road, since it's moving at the same speed. (00:18:25)
Visible crew/equipment: The camera crane is visible reflected in the glass when the army dudes are prepping a rocket launcher. This is the scene before everyone is sliding down the building.
Answer: the weapon is called an "Acid Rust Blaster" which seems to be similar to the cosmic rust seen in the animated series. the rust eats away at the Transformer's metal body.