I seem to recall audio inversion scrambling allowed on some VHF marine
channels. However, it also could have been a police agency using it also.
I know, not exactly the usage originally intended by the FCC, but trust me,
it has happened before on VHF marine. Although, with so many Nextels, etc.,
I am more likely to think a commercial marine operation using simple
scrambling. If you do a Google search or something similar and put in VHF
marine scrambling, you will see several manufacturers that offer scrambling
either standard or as an option. (You don't want other fisherman to know
where you caugh that sunfish at!)

Jim NØJS