As a formal member of the Brotherhood of Steel, you'll engage in various entry level Brotherhood quests for the team. Speak to Paladin Danse to initiate the quest.
Then initiate two other quests, the first Quartermastery quest and Cleansing the Commonwealth. Receive these from Scribe Haylen and Knight Rhys.
You can have both quests active at the same time, so you can minimize the back and forth between The Commonwealth and the police station. After reporting your successes to both Haylen and Rhys, Semper Invicta will be completed.