Dishonored Death of the Outsider - Salute! Trophy / Achievement Guide - Have a guard salute you [Bronze / 20G]

Mission 2
The earliest chance for this is in mission 2. You need to use the Semblance skill on a guard, preferably a veteran guard in red coat. Then walk past other guards (preferably in green coats) and wait for them to greet you. They will lift their hand to say hello. The trophy description is a bit misleading, they don't actually "salute" you, it's just a "hello" hand gesture they make.
The spot that worked best for me was in Shan Yun's house. You go there automatically, it's the main objective of the mission. In the lobby (immediately after entering the house) there's a red coat guard (woman). Use semblance, hide the body, make a manual save game, and walk in front of the patrolling guard while looking at him.

If he doesn't greet you, reload the save. Make the manual save immediately after using semblance on the red coat guard. This is completely random! The guards don't always greet you. It may take a few checkpoint reloads. Walk a little bit in front of the guard when he is also walking and look at him. Talking to the guard can also help triggering it, so try that if nothing else works.