The most important thing: NIOSH approval
The National Institute for Occupational Safety and Health is a part of the US Centers for Disease Control and Prevention that focuses on worker safety and health.
Before filtering facepiece respirators — a fancy term that includes N95 masks — can be used in any workplace, they must be certified by NIOSH.
For an N95 mask to get a NIOSH stamp of approval, it needs to filter at least 95% of airborne particles.
When finding out if an N95 mask is fake or not, NIOSH markings are your compass. But there’s some vetting you can do before you even have a mask in hand.