GIRLFRIEND: The American Sign Language (ASL) sign for "girlfriend"
If you are referring to a female friend, you could sign "FRIEND" or point to the person if they are in the area.

If you are referring to a female lover or beau, the concept of "GIRLFRIEND" can be signed a few different ways.

A common way to sign "girlfriend" is by signing "GIRL" + "FRIEND"

Another way to sign "girlfriend" is to compound the movements of each sign. (meaning each sign only does one movement instead of two)

A third way to sign "girlfriend" is with only one hand (this version is new)

Sample sentence: My girlfriend passed her firefighter exam.

Notes: 

See: PARTNER

See: HUSBAND

See: WIFE

See: FRIEND

See: BOYFRIEND

See: DATE