The CDC has a great page [1] on fake N95 masks, including details at the bottom on identifying real ones. They also provide a list of everyone who is approved to make them [2].

1. https://www.cdc.gov/niosh/npptl/usernotices/counterfeitResp....

2. https://www.cdc.gov/niosh/npptl/topics/respirators/disp_part...