A couple of people are doing me "favours" on the new boat. I can't find any mention of advertising restrictions in any class rules which technically (according to the ISAF rules) makes it illegal to display signage on the boat. Is there any history or precedent in the class?

History or precedent are not important - it's the rules that matter.

These are the rules:

ISAF Regulation 20

This part is the kicker and the reason I was after some history.

When the class rules or the rules of a System in force on 31 October 2008:
(a) prohibited the display of Advertising or did not prescribe about Advertising, such
rules shall be deemed to prohibit Advertising until they prescribe otherwise in
compliance with this Code;

Just put the sponsorship on.. If you read the penalties there is no mention of refusal of entry. Even if someone protests and you are DQ'd it will only give more exposure to your sponsors.

Thats not how I do things. I'm not looking to rattle cages just thank people who have helped out despite them not actually asking for it.

ISAF have got themselves into a bit of a knot there, trying not to upset anyone

The actual rule is that if a class does not prohibit advertising then it is allowed.
But, they say that a class with rules that did not "prescribe about advertising" in 2008 is considered to prohibit it until Dec 2012.

So although the Mosquito class has never been concerned enough about advertising to write anything in it's rules about advertising, we have now banned advertising in our class by simply not doing anything! Oops. Thanks ISAF!

The soonest the class rules could be changed to allow advertising would be January 2012, so I would suggest it's not worth going there just for the sake of the 11 months that it would affect.

I would just go ahead and decorate your boat (there's too many plain white Mosquitoes around as it is). Mosquitoes have carried advertising in the past. I don't see why anyone should want to start kicking up about it now.

Unless you plan on taking your boat to France. Just do it. No one is Aus is going to complain.
With any luck you might start a trend!!!