Asking too much?

What is it about some people and taking their shoes off when they come in your house? We have a couple of people who visit our house on a regular basis and never take off their shoes when they come inside. This is something that secretly drives me crazy. Our floor are very old wood floors that water stain easily. We also have light colored rugs scattered about. I have a small sign at the front door that asks people to remove their shoes. I don’t think this is too much to ask of people is it? It isn’t like I am at the door handing out disposable shoe covers or something. I simply want to keep the floors as clean as possible. The kids love to play on the floor and often put their faces on it. Taking shoes off at the door limits the grime that is tracked in and I believe lengthens the life of our rugs and floors. I always take my shoes off at other peoples houses. I am considering stopping this whenever I visit people’s houses who don’t reciprocate at my house. What do you think? I know it sounds a little petty but one person in particular thinks nothing of coming into our house with boots caked in mud and tromping through the whole house.