It's important to understand that prior knowledge, either personal experiences or education have a lot to do with the way someone responds to signs and the way they read them. We all tend to make associations of things we see/read to things we already know. Seeing always comes before words.
"It is seeing which establishes our place in the surrounding world; we explain that world with words, but words can never undo the fact that we are surrounded by it. The relation between what we see and what we know is never settled." -Berger, John
If you have any spare time check out the book "Ways of Seeing" by John Berger it is very interesting.