Meaning: without that annoying boot sound. Ok, it’s not that annoying for me since I rarely turn off my phone. But, if you turn it off a lot: it might be a little annoying.
So, how do you do it?
This is a pretty old trick: before you turn off your phone you set it to Vibrate only/Sound off, I use the quick settings menu for this where you can have Sound profile. Just tap it until you have Vibrate only/Sound off. That’s it. This have been tested on a HTC One with 4.3/Sense 5.5.
Turn off your phone, and when you start it again: it start directly without making ANY boot sound. Just remember to set Sound profile back to Normal when it’s started.