[paulk]

Solvents would be likely to damage the paint. A razor blade, carefully slid under the letters so as not to scratch the paint, may be the best way to go at them. Liquid soap, like DAWN, may be helpful. The regulations also call for a fine of $500 PER DAY for not following the requirements, so you may want to act quickly. (Though I doubt that the undermanned Coast Guard is sending people around measuring boat names and hailing port letters this week.)