These mission are the Plot, Detective and Contracts missions
You can only make the missions appear if you are dressed as the right persona.
There are 5 each and all of them take place in New Orleans, except for two of the Detective missions which take place in The Bayou.
The Plot = Lady
Detective = Slave
Contracts = Assassin
You do not need to fully synchronize them for any achievement if you find yourself having trouble with them
You can see how many of them you've done by going in the DNA - it's past the story + red E missions.