Well, being poked in the shoulder, despite from whom, is an assault consummated by battery.
Just because he's a police officer doesn't mean he can walk around jabbing his finger into people.
Moreover, many jurisdictions requires that police officers identify themselves when asked. Identification isn't usually "well, I'm a cop." You'll want to check your local/state laws on it, but it's generally something like they have to present you with a commission card showing they're a police officer if you specifically request it.
On that card will be the officer's name and status.
In some places, you may or may not have the right to deny them access to a guest log depending on what sort of business you are. However, the police generally can't come in and demand if the business isn't open without having a warrant that would allow them to come in and inspect files without the company's consent.