Signalling has an academic definition in economics, for sure. It's used both in an intentional sense ("workers signal their conscientiousness to employers by making their way through a 4-year college degree") and an unintentional sense ("being a high school dropout signals to the employer that a worker is in the bottom 5th percentile")

However, I do think LW uses it in a intellectual hipster sense as well - "Do you really think that, or are you just signalling?". The difference seems to me that instead of jockeying for economic advantage, we are accusing someone of jockeying for social status. Of course, such social jockeying is widespread, simply by dint of human nature. But I suppose we could replace this use of the word with "posturing" or something of the sort.