Yammer, which is some kind of enterprise social-networking service, put up this billboard in San Francisco this week. It strains for irony by taunting the very medium it's using—billboards being a prime example of one-way, old-media communication, which Yammer despises. But the ad doesn't make much sense. According to an e-mailed pitch, the sign, hanging above 5th and Townsend, "aims to demonstrate to passersby (and potential hires) that old methods of communication are becoming obsolete, and Yammer is ushering in a new standard." Yet this billboard will get Yammer more attention than anything they've ever done. That would be the opposite of futile and obsolete, wouldn't it?