Target Marks: Mission 3 | Target Marks Lost Planet Guide

On one of the crates at the beginning of the level.

On the right side of the fencing at the beginning of the level.

At the stairs that you reach after going across the snowplane.

On the snowplane (look closely at the screenshot to imagine the accurate location, it's near the cliff to the left of the field).

On a distant wall that you can see across the snowplane.

By the fence near where you later fight the boss.