@magigi citizen were spot on. The Rules are highlighted below:

THE TRAFFIC ACT
(Cap. 403)

THE TRAFFIC (AMENDMENT) RULES, 2012

General Information

1. A person may apply to the Registrar of Motor Vehicles to be issued with personalised number plates upon approval by the Registrar of Motor Vehicles and payment of the fees prescribed in the First schedule.
a)Registration of personalised number plates Kshs.1,000,000
b)Replacement of defaced or lost personalized number plate Kshs.50,000

2.Where a personalised registration number is transferred to another vehicle, an amount equivalent to two per cent of the fees payable for personalised registration fee under paragraph (1) shall be payable over and above the normal registration fee.

3.The following class of motor vehicles may not be issued with personalized identification plates.
a) Public Service Vehicle;
b) Cargo Trucks (private or for hire);
c) Service Vehicles (ambulance and funeral hearse);
d) Diplomatic Vehicles;
e) Tractor; and
f) Heavy machinery.

4.Where a person intends to use the personalized identification plates on another motor vehicle upon disposal of a vehicle which initially had a personalised identification plates, a retention certificate may be issued by the Registrar for a period not exceeding six months.

5.The personalised identification plates shall, where it is not used within the six months, be returned to the Registrar of Motor Vehicles for safe keeping.

6.Any person who uses unauthorized personalized number plates commits an offence and is liable on conviction to a fine not less than five hundred thousand shillings or on condition to imprisonment for a term not exceeding five years, or both.

7.The maximum number of characters shall be seven for each of the front and rear plates. The minimum number of characters shall be four on both front and rear plates. The characters on the number plates shall be in capital letters only.

8.Use of signs, symbols or any abusive words is strictly prohibited. The use of the letter “O” and “I” shall not be used unless they used in a complete word.

9.Both the front and rear plates shall be embossed in blue with a reflective white background.

10.The personalized identification plates shall not be transferable and shall when the vehicle is disposed, be surrendered and the vehicle re-registered.