A couple of our astute readers noticed strange symbols being painted on vacants around town and asked about them — we’re curious, too, so we asked around.

Apparently the red X means that firefighters should not enter the building if called to a fire, as the building is structurally unsound. Hopefully the city’s fire fighters are aware of this…
Update: Received this article from Reader BB, who is also a fire fighter. Thanks, BB, for the additional information!