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.

1623 and 1625 E. North Avenue

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!

Update:  Here’s more information from WBAL’s Jayne Miller.