Since it is winter time and many are not thinking much about the view outside how about marketing to offices and buildings that have interior windows (think conference rooms, etc) and market towards that type of cleaning for the next couple of months.
Too, drive around and check out the local stores that have painted their windows with holiday art, approach them and offer to was the art off so that they can rid themselves of one holiday and prep for another..... Speaking of which, are you at all artistic????? why not offer to paint valentines on windows and then you can clean those off at the end of February