The first 2 graffiti can you find in Rachel's room upstairs shortly after the beginning of episode 3.
The second graffiti is the planner on the right side of the desk beside the laptop.For a visual guide open the spoiler, inside you find my video with all 10 graffiti locations.
*** Spoiler - click to reveal ***00:08 - Optional Graffiti #1 (American Graffiti)
00:43 - Optional Graffiti #2 (Extra Credit)
01:16 - Optional Graffiti #3 (Peer Review)
02:05 - Optional Graffiti #4 (Monthly Masterpiece)
02:53 - Optional Graffiti #5 (Spit Take)
04:38 - Optional Graffiti #7 (Hello Nurse)
05:26 - Optional Graffiti #6 (Venting Machine)
06:53 - Optional Graffiti #8 (A Penned Appendage)
07:57 - Optional Graffiti #9 (Drunk Drawer)
08:41 - Optional Graffiti #10 (Messed Up)