I think it's important to talk with others, adults and kids, on the playground. This is how we get to know people so that we can be comfortable with them. If you're frequently on the same playground, notice other parents who are also often there and make a point of talking with them. This will cut down on the number of cold stares.
Yes, I've also noticed that some parents worry that there child is bothering me. That irritates me more than the child who does end up over staying their welcome while talking with me. I've learned ways to redirect the child who stays too long. But I've yet to have a parent relax when I say that's OK. I enjoy talking with your child. It's as if there is some unspoken code that says the child's parent has to protect everyone from their child.
I believe that if the parent doesn't want to talk with my child, they'll redirect the child away. One way that I do that is to suggest that they go swing or that they find my child or another child that I've with whom I've noticed them playing. If that doesn't work, I look at the other parent and suggest the child go find mommy. If the other parent is watching they pick up on the cue and come get their child or the child does as I ask. It all works out.
I've made some good "playground" friends of parents by being friendly myself. I like the inter action. I pick up on the cues of the silent parent who wants to be alone. It's all about social interaction.
I've not had anyone give me mad looks. Sometimes questioning looks, like is this OK? I would feel sad that a parent would just look mad or anxious or ? and not just come over and talk with me. This would make me sad. Community is so important and they're not allowing it to happen. I'm disappointed and sad when parents apologize for their child talking with me. They're giving both me and their child a negative message; that their child is a bother. I think this affects the child so that they will feel like a bother instead of the precious and interesting child that they are. And the message to me is that they judge me to be bothered. It doesn't matter how I actually feel. So both of us, their child and I, are unimportant.
Perhaps this happens to you because you're not there very often or the neighborhood is not as safe as some? Or they are passing judgment on you as not wanting to be bothered. My solution of something to try is to talk with them. If they're calling from across the way, go over and let them get to know you.