hey in the UK... the first letter represents what year the car was registered.
e.g
a - 83- 84
b - 84- 85
c - 85- 86
d - 86- 87
e - 87- 88
f - 88- 89
g - 89- 90
h - 90- 91
j - 91- 92
k - 91- 93
l - 93- 94
m - 94- 95
n - 95- 96
p -96 - 97
(it changed a bit later to every 6 months and finished the alphabet and now we have a system of numbers.)