A totem pole is often used (inaccurately) as a catch-all term to describe different types of advertising and branded signage which are monitored by planning departments, including those at service stations.
A monopole is a single, tall pole, with a brand logo attached to the top of it. It is designed to be clearly visible to passing traffic. The logo at the top is most often that of a fast food brand, like McDonald's or Burger King, but it has also been used to promote WHSmith.
If the pole is only on one side of the sign, as was common with Esso, then it can also be known as a flag. This is not to be mixed up with an actual flag, which can also be used in advertising, usually known as a flagpole.
A monolith is a narrow sign, just like the old stone monuments with the same name. Tall monoliths tend to be found by the main road, while smaller ones have become more common by the main entrance.
Strictly speaking, a monolith has a firm, wide, base, while a totem pole will be fixed to the ground with two poles and a gap in between them. Understandably people don't take time to inspect the base of the sign, so 'totem pole' and 'monolith' are often used interchangeably.
The main identification symbol (MID) could be either of the examples above. It is a phrase normally only associated with petrol stations, where there will generally just be one sign next to the road identifying the brand of fuel and its facilities.
A goal post is a very tall totem pole: a big, wide sign tall enough for people to walk between the legs. Moto introduced them nationwide as part of their branding strategy in 2001, but found they weren't getting much use and have started removing them.