This past weekend while showing houses my buyer and I decided to stop by a nearby Open House. Inside was the listing agent and several other people viewing the home. I introduced myself as a Realtor and let the other agent know that my buyers and I were going to take a look around. When we were done the listing agent was insistent on me and my buyers signing in.
The purpose of the Open House sheet is for the listing agent to grab names, email addresses and phone numbers. So he can call them and generate future business.
The seller doesn't need a copy of the sign in sheet and has no use of retaining one.
It makes no sense why the listing agent would want me to sign in for his open house. I don't want or need his seller to call me. He shouldn't want his seller to call me either. Additionally, I don't need or want he or his seller calling my buyer. That doesn't make sense either. If I have more questions about the property I will contact the listing agent. I don't want anyone following up with me.
There is no law or rule that says you are required to sign in at an open house. I don't require anyone to sign in at my open houses. I might ask, but I never stand in front of them like it's about cause a problem if they don't. If you feel it's rude to not sign in then that's your choice to follow the request of the listing agent.
Again, the only reason you are asked to sign in is so someone can sell you later... or at least try to.