lgrov44 wrote:
Scratch Wiki wrote:
In 3.0, this feature has been replaced with a hashtag system; preceding a word with a hashtag automatically creates a link to the search results for that word.
As far as I'm aware, this is all it really does, though you can learn more if you wish.

It also makes the project appear in the search results for that word and in the relevant section of the Explore Page (Animations, Art, Games, …). Including the word in the project description, without the #, has the same effect.