Usually when you are anywhere nearby when a 50 BMG is being shot you would be aware of its presences by the loud sound, but thanks to a suppresser, you may not recognize the sound of this rifle.
Many know the 50 BMG shot to be one of the loudest and most painful out there. Whether you are are the shooter or not, if you are anywhere in the vicinity you will hear, and most likely, feel the shot go off.
Unless, that particular firearm is both suppressed and shooting subsonic ammo. Then you might just think someone is out plinking with an airsoft rifle. Don’t think so?, go to 3:13 on the video to hear the differences between suppressed and unsuppressed.
Although, of course, you don’t quite get the full effect of the sound difference by watching the video, you can definitely tell that there is a big, big difference. Just the fact that the shooter was able to take a shot without hearing protection and then still talk in a normal voice afterwards should be enough to convince most people of the suppressor’s effectiveness.
Sources: Ohio Outdoor Journal, C Buckner