The term throw up comes from the fact that the bomb is just thrown up on a wall, bus, train, etc very quickly.
ii.You know that kid who throws up NE, what do they write?
Throw up also called a throwie or throw.
Throw ups are often only one or two colors, and are a very unembellished symbol, letter, abbreviation, or short word.
Taggers (people who tag) often throw up a tag like this everywhere they go.