Not sure if you have heard about this or not but here it is. As of the 1st May 2008 it will be compulsory to display the Northern Ireland MOT discs. Below I have copied the section from the dvtani web site.
Mandatory display of MOT Disc from 1st May 2008
From 1 May 2008 an amendment to the Motor Vehicle Testing Regulations is introducing mandatory display of vehicle test certificates (MOTs).
In 2001 the Driver & Vehicle Agency introduced a new two-part vehicle test certificate for cars and motorcycles. Part two of the vehicle test certificate (the disc) should be displayed on the inside of the windscreen. It should be placed on the passenger's side and should be close to the edge of the windscreen, so as not to cause an obstruction to the driver's view of the road.
In the case of motorcycles the certificate should be displayed on the nearside of the motorcycle in a weatherproof container.
Failure to display the disc will be an offence and may result in a fine of up to £200.
Should you require any further help or advice on this subject please contact us on the number below.
Tel No: 028 9025 4171
Fax No: 028 9025 4407