Prostitutes don't wear uniforms or anything else at all so it could be impossible to prosecute or prove except through the transfer of funds evidence or what have you by computer which makes it even more exclusive as well during Trek's time.
What I'm interested in is if you're allowed to have holographic or robot spouses like the EMH Doctor or Data? That raises a whole bunch of cans of worms. You could have a harum of holograms or robots who are prostitutes by night and criminals by day. They would probably be very expensive too, assuming that they are working for the equivelent of money in Star Trek's time, or for power or information, manipulation, domination, etc., etc.. Vogayer's EMH was getting married in 'End Game' and Data dated.