It means a merge has spotted a possible twin – someone who looks like they might be the same person as this one. Press Merge them to start the merge page, or They're not the same person to send the box packing. For example, after merging Grandad's two records, the tree might notice two records for Grandma that look alike and ask you about them.
Where to find it
Person page → the box saying they might be the same person as someone else
Only people with the "Edit" tick.
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