Logo lights, when installed, are part of the Aircraft system. As such there are Airworthiness considerations, as in any lighting system, when they go wrong. The ANO dictates the lighting ‘must haves’ and the MEL time periods reflect the importance of the systems. Logo lights with a 120 day period are, obviously, not very important in the grand scheme of thing but are still Airworthiness items whether or not they are mentioned in the ANO.
It is my understanding that the MMEL is produced by the Manufacturer. From this the Operators can produce their own MEL that must be as, or more, restrictive than the MMEL. This MEL must pass scrutiny by the Operators NAA so that regional differences are incorporated.
p.s. Big Bad D. If you have the opportunity, can you do some modifications on the A320 series logo lights? Increasing the length of the connecting wires would be a good start. Playing ‘dropsy’ with the attaching screws to the SBU falling into the cavity below is no fun on cold and windy nights and more than doubles the time of the job as you have to remove the lower surface panel to remove these screws! 
Last edited by morton; 24th October 2008 at 15:44.
Reason: Noticed Big Bad D was a designer