In the first room, with the shield that the Bosun uses to block your way, head north to the room with the elevator shaft and jump pad. Use that jump pad and at the top, go behind the yellow pipes to your west, where you’ll spot the symbol on the floor.
From the last symbol, continue into the next room, which is outside and go on the west ledge, bypassing the jump pad (leads to Crew Quarters area). If you look slightly southwest, you should see another area you usually pass through the first time through the zone (Starboard Ascent). You want to jump onto the uppermost ledge here, where you’ll find the symbol on the southern wall. Note that there’s a red loot chest here that is one of the three hidden ones for the Bosun’s Mate challenge.
Alternatively, if you’re on the lower section of Starboard Ascent, you can reach the ledge with the vault symbol by using the thin portion of the wall on the eastern side of the area.
Go to the engine room at the far north end of the map and get to the highest point via jump pad on the north side. Your goal is the catwalk at the very top on the southern side, so use the large pipe on the eastern side to get to the catwalk. You’ll find the symbol on the eastern end of the thing sticking out of the wall.