A recent decision by the North Carolina Court of Appeals suggests that it is. However, UNC School of Government Professor Jeff Welty has his doubts:

Last week … a divided panel of the court of appeals held that a trooper properly stopped a vehicle “after witnessing . . . a passenger in [the] vehicle . . . extend his middle finger in the trooper’s general direction.” The majority acknowledged that “there are a number of decisions from courts across the country [holding] that one cannot be held criminally liable for simply raising his middle finger at an officer.” Yet it ruled that the defendant’s conduct provided reasonable suspicion of criminal activity, namely, disorderly conduct. …

I’m skeptical. The state didn’t even try to argue that the stop was justified on that basis. It argued only that the stop was proper under the community caretaking doctrine, a contention that didn’t persuade any of the judges on the court of appeals. More importantly, as the majority acknowledged, there is a substantial amount of case law holding that flipping off an officer isn’t criminal. …

The majority points out that conduct that isn’t itself criminal may provide reasonable suspicion of criminal activity. Certainly, sometimes an investigation of ambiguous conduct unearths additional evidence of a crime. But what’s to investigate in a case like this one? The officer saw all the pertinent facts unfold before his eyes. Either shooting an officer the bird is a crime or it isn’t, and further investigation seems extremely unlikely to uncover new evidence to support or dispel the possible disorderly conduct charge.

There’s lots more information and discussion in the blog post, including a link to this article about the history of the one-finger salute.