You can be sure if the FBI was really there in a van, they wouldn't be broadcasting "FBI van" as a SSI.
As far as Federal law goes, it's only illegal to pretend to be a law enforcement officer if you're trying to get someone to do something fraudulently (taking their clothes off, turning drugs or money, over to you, etc...).
Iowa makes it illegal for a person to pretend to be a police officer without proper authority, but neither a "van" nor a "wifi" is a person. The law is again rarely enforced unless someone uses it to get someone else to act under the belief that they are (that they pulled them over or otherwise detained them, tried to extract money, free food, or discounts, etc... ).