Where I live, one of the most common categories of sky object without a weird obsessive spotting community is "lost birthday party balloons," so that might be a good choice—although you risk angering the marine wildlife people, and they have sharks.

"Sky Spotters", by Randall Munroe, licensed under Creative Commons Attribution-NonCommercial 2.5 License

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Where I live, one of the most common categories of sky object without a weird obsessive spotting community is "lost birthday party balloons," so that might be a good choice—although you risk angering the marine wildlife people, and they have sharks.