Within the school, Lincoln encounters hallucinogenic smoke that can restrict his movement and weapon usage. You must use the black light to find specific symbols, such as the "mark of the blessed".
If you are looking for a guide specifically for the "Part 3" section of this DLC, it typically covers the following mission segments: Mafia.III.Sign.of.the.Times.part03.rar
After completing the main story, you can invest money to rebuild Sammy's Bar. Part 3 Walkthrough Highlights Within the school