Well, these letters are Suzuki factory codes for their bikes as they call it, the VDS (Vehicle Description Sector). Each mean something in connection with the design. Look...

First letter (category):

C = Scooter
B = Business model, commuter
N = Single cylinder sport street <---LS 650
G = Multiple cylinder sport street
F = Family
S = Off-road
V = V-type engine, street (V2, V4)
H = Square Four

Second letter (displacement):

A = —49cc
B = 50—69cc
C = 70—79cc
D = 80—89cc
E = 90—99cc
F =100—124cc
G = 125—149cc
H = 150—199cc
J = 200—249cc
K = 250—399cc
M = 400—499cc
N = 500—599cc
P = 600—699cc <---LS 650
R = 700—749cc
S = 750—849cc
T = 850—999cc
U = 1000—1099cc
V = 1100—1199cc
W = 1200—1299cc
X = 1300—1399cc
Y = 1400—1499cc
Z = 1500+

Third character (engine configuration)

1 = 2-stroke, single
2 = 2-stroke, twin
3 = 2-stroke, triple or four
4 = 4-stroke, single <--- LS 650
5 = 4-stroke, twin
6 =  -
7 = 4-stroke, four

Fourth character (model version, design sequence):

1: refers first version <----LS 650
Further numbers or letters used after 9 show further modification in the model.

Fifth character (model variation):

A = non restricted, full output <--- LS 650
Further characters are used for special editions.

Hope this helps, because it lasted for a while to type in...

Source: suzukicycles.org