No: Teams does not support hashtags, at least not yet, in a way Twitter or Yammer uses them.
Yes: You can use hashtags, but you need to put some personal effort there (agreed) hashtags.
How: add desired hashtags to content so you can use these hashtags in search. You can add them to discussions, OneNotes or inside documents too (if you so wish to – but usually just include the document in Teams discussion and use hashtag in there).
Why: Hashtags can combine information from different topics and teams into one search result. You can even use these in private chats.
No: It won’t show you anything from any team you are not member of. And it won’t return any results from private chats unless you are a chat participant It does not search inside calendar meetings.
Benefit: You can find some content, like chats, using hashtags in search.
As we all know Team’s search needs improvements – however with hashtags the search works really nicely. Of course if you can use Microsoft Search then the results are nicely in one view.
The drawback: you need to use same hashtags as everyone else. If you stick to few well known topics (#Microsoft365, #ProjectName, #HRNews) that can help surfacing some information.
Vesa Nopanen - My Metaverse Day 
Hey Tony.
we have developed a Microsoft Teams App to have now a „real“ tagging functionality for messages – https://www.smarterbusiness.at/en/tagging-for-your-messages-in-microsoft-teams. So you will be able to specify your tags for your teams and all users can use them with mentions or with the message extension. what you think about this functionality? Would be cool if you will try it out when we have it in the AppSource catalogue 🙂
Greetings from Austria.
LikeLike
Hi Tony, thanks for the article. It might be worth noting that searches in MS Teams do not pay any attention to the “#” character, so searching for “#hashtag” will find content matching “#hashtag” or “hashtag” or even “hashtags”. So including the # symbol in content doesn’t gain us much, except perhaps the visual reminder that this is a keyword that might be worth searching for. I hope that MS eventually will improve this. –Jon
LikeLike