George, you are not seeing things--this is a common occurrence, both up there (where I'm from) and here in southeastern Wisconsin (where I live now)--I see political signs on overpasses a lot, as they're highly visible to motorists. I'm not sure what permissions are needed to do this, but it happens all the time.
Am I seeing things or are those political placards on the trestle?If they are somebody's being very creative or very funny!
This bridge is owned and maintained by the CN with BNSF having trackage rights over it. The bridge was built by the Duluth, Missabe & Northern Railway. (The DM&N became part of the DM&IR which is now part of the CN.)
Thanks for responding,Matt.Got to admit it is weird posting signs all of the way up on the top of that bridge.I just happened to notice it being that I look at bridges in pictures.