how to disable spring boot logo in stdout?

http://docs.spring.io/spring-boot/docs/current-SNAPSHOT/reference/htmlsingle/#boot-features-banner

new SpringApplicationBuilder()
    .showBanner(false)
    .sources(Parent.class)
    .child(Application.class)
    .run(args);

Edit
In the newer versions of spring boot(current is 1.3.3) the way to do it is:

1) application.properties

spring.main.banner-mode=off

2) application.yml

spring:
    main:
        banner-mode: "off"

3) main method

public static void main(String[] args) {
    SpringApplication app = new SpringApplication(MySpringConfiguration.class);
    app.setBannerMode(Banner.Mode.OFF);
    app.run(args);
}

Docs

Edit:

To change this with and environment variable use the property with underscore instead of dot. Try:

SPRING_MAIN_BANNER-MODE=off

See the docs for externalized config.