Talk:Sigils/@comment-26909334-20150820225352/@comment-3336377-20150824000617

https://forums.warframe.com/index.php?/topic/499137-hotfix-1701/

"Players can now purchase the Lotus Heart Sigil from the Arsenal (Regalia Section) for 1 Credit."

- Hotfix 17.0.1 Patch Notes

It's still available, and it's dirt cheep. Go grab one while you can.