That would be one of the advantages of being able to check in with VTS. The captain and pilot would be aware of the fact that you were making the crossing and would know where you were headed. Having that knowledge they might not feel the need to sound the danger signal.
Working as a mate on tugboats, well before sea kayaks were around in any kind of number and before VHF radios, it was the sailboats we had the hard time with. The biggest problem was not knowing where they were headed. Just to be sure, they were often given the 4 or more blasts of the horn. Much easier to make sure they were aware of us than to try to avoid collision a few minutes later. I would guess that's the reason you receive the warning blasts.
Sea Kayaker Magazine