Leaving a face down penny tip

I've never worked in the restaurant industry, but my girlfriend has. Much of her terminology and simple restaurant operations are new to me. During dinner and some poor service the conversation of tipping came up and leaving a face down penny.

When service at a restaurant is horrible, one of the worst tips you can leave is a downward facing penny. With Abe looking down, the penny is disrespecting the server. This is considered worse then no tip, as the server has to deal with a random penny left behind.

I couldn't find much information on this topic, however I read an alternative version. Leave two pennies, one face down and one face up representing their first change. Second time if the service is the same, you leave two pennies face down.

Time for dinner... hoping to have some face up service. Restaurant