I think the way the media generally covered the story, it sounded like people were putting out a real pumpkin with a sign. Frankly, I think putting up the pumpkin does create confusion.
Because kids tend to 'Trick or Treat' at night when it's dark and signs are hard to read at night. Then you add in that kids don't really take the time out to read(provided they can read)when all they really care about is the candy behind the door. There's also the problem of kids having to look through plastic masks where their vision is already a bit hampered.
After you've seen a few dozen pumpkin displays I would imagine you stop seeing the verbiage on the pumpkin.