In F1 today you have 22 cars lined up on the grid with a set of numbers on them that pretty much have no meaning to anyone but the officials.
A problem that I noticed at the Australian Grand Prix a few weeks ago was that people were sporting merchandise which seemed odd in todays context, such as "Massa #6" on the back of a Ferrari jumper, when this year it is his team-mate who is sporting that number.
Call me silly, but wouldn't it make much more marketing sense (as well as common sense) if driver's weren't chopping and changing numbers every season? Personally, I would be much more reassured if I spent $150 on a team jacket which at least had the drivers numbers on it which were applicable for more than one season. The only team in recent years to actually have benefited from this was Ferrari gear from 2001-2005.
At the moment, driver numbers are basically useless as they basically have no marketing value whatsoever. Personally I don't see why the FIA don't just go back to the system where each team is designated 2 numbers. Fans would actually be able to instantly recognise the numbers and be able to draw links to each driver from those numbers.
Or better still, let each driver choose his own racing number, which is applicable no matter what team they drive for. Look at how recognisable Valentino Rossi and teh late Dale Earnhardt are by their racing numbers alone.
It is simple, but it would be mighty effective, for both fans and merchandise buyers.