At the time I wrote my original list many years ago MLS was listed as an unknown British WWI helmet manufacturer. Link to my original posting on manufactures and their codes.
http://www.treasurenet.com/forums/militaria-arms/288546-m1917-helmet.html
Known steel suppliers of the WWI British helmets:
FS = T. Firth & Sons Ltd Sept 1916 – 1918
BS = W. Beardmore & Co Ltd Jan. 1916 – 1919
HS = Hadfield Ltd Jan. 1916 – 1919
V = Vickers Ltd 1916 – 1917
MS = Miris Steel Co. Ltd 1916 – 1917
A = Edgar Allen and Co. Ltd 1916 – 1918
F = Thomas Firth and Sons 1916 – 1918
O = Samuel Osborne & Co Ltd. 1916 – 1918
B = Bury's & Co. 1916 – 1918
Known makers of the WWI British helmets:
D = James Dixon & Sons Dec. 1915
HW = Hutton & Sons Dec. 1915
HH = Harrison Bros. & Howson Ltd. Dec. 1915
M = J&J Maxfield & sons Dec. 1915
R = John Round & Sons 1916
V = W&E Viener Dec. 1915
MLS = ?
FKS = Possibly Thomas Firth & Son
M&S = Possibly Maxfield & Sons.
Known makers of the WWII British helmets:
BMB = Briggs Motor Bodies Ltd of Dagenham
F&L = Fisher & Ludlow Ltd of Birmingham
GSW DP & H = General Steel Wares Department of Pensions & Health
HELMETS LTD = Helmets Ltd of Weathhampstead
RO&Co = Rubery Owen Co Ltd of Leeds (Spelled as RO CO or RO&CO)
WD = William Dobson & Son of Birmingham
PPM = Patent Pulp Manufacturing Co Ltd
(Updated)
JSS = Joseph Sankey & Sons