I wrote about this phenomenon years ago in Omniveillance:

 Immersive Labs, a company in Manhattan, has developed software for digital billboards using cameras to gauge the age range, sex and attention level of a passer-by. The smart signs, scheduled to roll out this month in Los Angeles, San Francisco and New York, deliver ads based on consumers’ demographics. In other words, the system is smart enough to display, say, a Gillette ad to a male passer-by rather than an ad for Tampax.