Green’s Dictionary of Slang

banner n.

[SE banner, a flag]

1. [18C] the pubic hair [in this context the ‘flag’ displayed by the genitals].

2. [late 19C+] (US tramp) a bedroll [one ‘unfurls’ it].

3. [1930s–40s] (US prison) a report citing a violation of prison regulations.

In phrases

carry the banner (v.) [pack v.1 (1)] (US)

1. [late 19C+] (also pack the banner, carry the stick) to walk the streets as a tramp; thus banner-carrier n.

2. [1920s–30s] to sleep rough, esp. of the thousands of homeless children who were forced to sleep in the New York streets.

3. [1930s] to live as a tramp.

flag the banner (v.)

[1940s] (UK Und./gay) of a male prostitute, to solicit.

get oneself a banner (v.)

[1940s–50s] (US Und.) to move from the general prison population into protective solitary confinement.