Similarly ancient request for super useful feature on Signal:

Ability to mark messages or media as NSFW / confidential / spoiler
https://community.signalusers.org/t/ability-to-mark-messages-or-media-as-nsfw-confidential-spoiler/4358

I find this very useful on Telegram and here on the Fediverse. Add your fav/heart if you're into it, and leave a comment if you're REALLY into it. :D