Schnell,
I usually just ignore them, but before I do that, I see that shit and I storm into this weird internalized rage where I start writing a response and deleting it. Anything I say is just going to fly over my mother's or MIL's head and then she'll get mad, so why bother?
I too go through writing fits when something irks me big time. Once, I wrote a flyer against the JWs and distributed to my entire apartment complex. There's over a hundred units and 90% of them are either JWs, inactives and disfellowshipped ones.
Let me ask you, are your letters long?