Where does “знаменовать” come from?

знаменовать (Russian) comes from Russian знамя, from Proto-Slavic znamę, from Proto-Indo-European ǵneh₃men.

Ancestry of “знаменовать”, step by step

Step	Language	Word	Meaning
1	Russian	знамя	standard, banner, flag, colors, ensign
2	Proto-Slavic	znamę	sign
3	Proto-Indo-European	ǵneh₃men	—

знаменовать — Etymology, Origin & Word History | Etymology Explorer