We are very lucky to live near many neighbor kids. My kids constantly want to play with the neighbor kids, but we never know if they can play or not. I don't like sending them over to ask too frequently. And the neighbor kids ring our doorbell a lot, which makes my dogs bark a lot! So we found a solution that I hope will work now that the kids are out of school for summer.
I wanted to make nicer ones, but the kids really wanted to help, so this is what we made. We have several non-readers in the group, so we made them universal. All have a large "X" if they can't play and a smiley face if they can. We passed them out to each of the neighbors. I'd have to say, I like the success we have had so far.
You can make your own with items you have on hand, let the kids decorate and then give them out to their friends!