Nah, I don't buy it. In one of my fave books, "intelligent life in the universe", it makes mention that although Scott Carpenter could see chimney smoke and foot trails in Tibet, he could find no trace of Los Angeles. Alien smog, alien weather, and vee are squared conspire to reduce the flux from city light on other planets to a value too low to bother with, I bet. OTOH, that same book postulated what our planets' spectrum might look like from an observatory on Mars, and after crunching the numbers, the authors concluded that any astronomer from that vantage point would have no trouble at all seeing an increase in light from sodium and mercury vapor, apparenty increasing from nothing to quite a lot over just the last several decades. But over interstellar distances? Man, I just don't think so. Not that it hurts to look. I just think that there may be other light signatures that would be easier to spot. The exhaust from a Bussard ramjet pointing our way, fr'instance. I bet there's some photons coming outta that bad boy.