J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Sail Number

That's the reason many regattas provide stick on bow decals. For one-design, it shouldn't be a problem unless somebody is coincidentally using sail numbers from somebody else's hull number who is also racing.

Then you have a special case like Pale Rider sailing in the schizophrenic mode - the bow thinks it's Rhapsody and the stern Pale Rider