According to Wikipedia, "Film noir is a cinematic term used primarily to describe stylish Hollywood crime dramas, particularly those that emphasize moral ambiguity and sexual motivation. Hollywood's classic film noir period is generally regarded as stretching from the early 1940s to the late 1950s. Film noir of this era is associated with a low-key black-and-white visual style that has roots in German Expressionist cinematography, while many of the prototypical stories and much of the attitude of classic noir derive from the hardboiled school of crime fiction that emerged in the United States during the Depression."
The Wikipedia entry goes on to examine film noir's prehistory, especially it's origins in 1920's German film. Brooks, of course, made her two greatest films in Germany at the end of the silent film era. Each of those films, Pandora's Box and Diary of a Lost Girl, were released in 1929. For me, that historical stylistic connection doesn't really define Brooks as a film noir actress.
Nevertheless, just today, I came across a stylishly done youtube video - an elegant homage by "Rob in L.A." to some of the iconic femmes-noir. Included are two clips featuring Brooks (the only actress included twice); it also includes a clip of Clara Bow, the only other silent film star. (Early stars Anna May Wong and Marlene Dietrich are also included, but in clips from talkies.) The video is set to a haunting rendition of "Angel Eyes" by Bruce Springsteen.
A couple years back, film noir author and expert Eddie Muller told me about a film noir film he was working on featuring a Louise Brooks inspired character. I wonder what happened to it?