I am sure you are all wrong. This is a warning to Pilots of low flying planes (hence the standard street sign) that they are at risk of being shot down by suspicious black cars. Notice the explosion and projectile path. This sign must be in an area where there is a high rate of car vs. plane drive by shootings.

Warning, Close cover before striking

ballot box, the piece of wood inserted in the top is intended to push the ballot into the box ( at this point little trolls go to work)

This is obviously a primitive periscope