This is similar to many other professions that display letters, photos of sold items, photos of clients, testimonials etc on their site, or within their office. It is just a way to say - "hey, look I did it before, here are some examples"
That being said it is your house, and I would respect a clients wishes, they may be able to modify the detail and keep the price, neighborhood and date.
I just think that I've been gracious enough with allowing the sign to remain on my lawn and believe that along with the website photo should be done with by now. While it is a public record I don't believe I owe it to the agency to keep letting my home be an advertisement for them.