Masks in Watch Dogs: legion are clothing items that are used by characters to hide their identity.
Masks
Locations on London
1
Albion Internment Centre
Restricted area (Albion).
2Brixton Barrier Block
3Brixton Recreation Centre
Show the map
4Broca Tech
Show the map
5Buckingham Palace Gardens
Show the map
6Camden Market
7Cemetery Park
Show the map
8DedSec Safehouse
It's in the safehouse.
9Downing Street
Restricted area (Albion, Police Officers).
10Embassy Garden
Public access.
11European Processing Centre
You can get to the tower where the box is placed from the garden side.
12FoodTown
Show the map
13Limehouse Garden
Public access.
14London Bridge
Public access.
15London Bridge (Secret)
You can get here through a secret passage located to the west of the bridge which opens at 2:00 AM!
16London Carriage Service
Restricted area (Albion).
17Mask
Show the map
18Mask
Show the map
19Mask
Show the map
20Mask
Show the map
21Mask
Show the map
22MI-6 Building
Restricted area (Albion).
23Museum of the Home
Public access.
24New Scotland Yard
Show the map
25Perry Harris Redevelopment
Restricted area (Construction Workers, Clan Kelley).
26Rotherhithe Docks
Restricted area (Construction Workers, Clan Kelley). You can easily get here from the water side.
27Somerset House
Restricted area (Albion).
28Southwark Incinerator
Restricted area (Clan Kelley).
29St. Pancras International
Restricted area (Albion). The box is located in the control room on the upper floor of the prison section.
30St. Paul's Cathedral
Public access.
31The Battersea
Restricted area (Albion).
32The Martlet's Nest
33The Roberts & Scott Hall
Public access.
34The Sandstone Residence
Restricted area (Clan Kelley). The box is in the security room you visit during the mission "Bloody Mary Kelley".
35The Xcess
36Thorne's Felts
Restricted area (Clan Kelley).
37Walkie Talkie
Public access. You must visit the room where the mask is during the mission "Initiate Sequence".
38World of Tomorrow
Restricted area (Clan Kelley).