[G3E9]

I use camel case when the subject needs two words in order to identify it. Underscores, I feel, can be used to separate and include multiple ideas within a single name, in order to explain or emphasize on a relationship.

country_state_city

or

unitedStates_texas_houston

or

unitedStates_newMexico_santaFe

edit: sorry, don't know HN's markup