What is a "show" in petroleum geology?
A show is a visual indication of hydrocarbons, in the jargon of petroleum exploration, it is typically used to describe a drilling. It could be e.g. a Gas show in the drilling fluid. Show evaluation is an important tool to understand a reservoir. 

When hydrocarbons reach the surface naturally, we call it a petrolium seep. 

Technically, I guess, a seep could be a show if it's used to map a play but I never heard the term used in that context.