For this trophy you will need to obtain 5 Silent Assassin Ratings on the hardest difficulty of the game i.e Professional Mode. The trophy will pop upon completing your 5th mission with the Silent Assassin Rating. Also note that this trophy will also unlock 5 Normal Silent Assassins and 5 Expert Silent Assassins because the difficulty trophies stack. See Silent Assassin for an explanation and tips on how to achieve the rating.
You do not have to get the rating in consecutive missions but do bear in mind that you will have to get the rating on 5 separate levels, unlike in Silent Assassin and Contracts you can not simply redo the same mission 5 times. Five of the most easiest missions to get the rating in are:
Mission 6: You Better Watch Out
Mission 8: Till Death do us Part
See the Hitman Blood Money - Professional Guide for a a video/written guide on how to get the Silent Assassin Rating for those missions.