Ah but yes, Mister Faldage, a red light is indeed a word and a pretty emphatic one at that. A red light is a symbol just like these words I write are symbols and they don't exist in a vacuum, they only exist as "words" in the context of our culture. For example take Egyptian hieroglyphics, they are not words until the moment of decipher. Until that moment they are mere pictures and markings. This is because the referent constitutes and gives essence to "wordness" and not the medium itself.
So whether spoken or written, or inferred from a menacing growl, a transfer of meaning from the symbol to the recipient determines that which is a bona fide word.
Now a further example...
It is said that "amemeba is flexanimous". Now tear off the word
flexanimous from this sentence and put it in your pocket if you are not sure what it means.
As the paper with
flexanimous written upon it rides about in your pocket you will never know if it is a real word or not until you google it or ask tsuwm.
See?
