@MartinSleziak When that question was deleted, the tag siegel-zero was removed, too.

SEDE shows it as the only deleted question with that tag: data.stackexchange.com/mathoverflow/query/858309/… (So most likely the tag was still there when it was deleted.)

Congratulations to YCor on earning the gold Copy Editor badge.

It is clear that YCor puts a lot of effort into improving the content of the site. This certainly does not go unnoticed - and the badge is probably at least a symbolic reward.