police van vs black Maria

police van and black Maria both are nouns.

Word	Noun	Adjective	Verb	Adverb
police van	Yes	No	No	No
black Maria	Yes	No	No	No

As nouns, police van and black Maria are synonyms defined as:

Other synonyms of police van include paddy wagon, patrol wagon, police wagon, wagon.

police van (noun)	black Maria (noun)
van used by police to transport prisoners	van used by police to transport prisoners