Air carrier technician reported while replacing a nose landing gear tire on a B737-800; they heard the hydraulics come on after they briefed the flight crew to not turn on hydraulics.

Narrative

On a turn; I found the rh nlg tire had a cut on the sidewall. I went upstairs to get the gear pins and asked the pilot who was in the jet bridge if he was the outbound crew. He said he was; so I told him we were going to be changing the nlg tire and to please not turn on hydraulics. He verbally confirmed and proceeded to accomplish his walk around. I then placed the maintenance safety chart on the center pedestal opened to the 'do not operate hydraulics' page and grabbed the landing gear lock out pins. I installed the gear pins; and the nlg steering bypass pin was already installed by ramp crew since this aircraft was on an hour turn. My coworker and I changed the tire. My coworker stated he heard the hydraulics come on while I was getting the new tire; but noted he was safe.When I went upstairs to question the pilots about the hydraulic system; they were taking a photo with onboarding passengers in the flight deck. When the passengers left the flight deck; I found they had moved the maintenance safety chart. I asked the copilot why the hydraulics were on as I had placed the flip chart and briefed the captain. He said he didn't know what the flip chart meant; and asked where it was displayed. I showed him how I had placed it and explained that we were doing a nlg tire and for our safety I had put that chart there so they wouldn't pressurize hydraulics; and by turning them on; he could have injured us. He never apologized or attempted to correct the issue by depressurizing. I handed the chart back to him to restow behind his seat. I noticed him flipping through it; so I asked if he'd ever seen it before. He said 'no'. Suggested Resolution: Please educate flight crew on maintenance safety charts and their purpose.