@Erstwhile @melvin I wrote a whole long piece on this, peppered with #hashtags (in which all you do is add a # before a word while typing) before trying to correct it and messing up a Delete and Redraft!
Here's a (slightly) shorter version:
The symbol goes back to #roman times. Was called #Pound for a long time. Originally an abbreviation of lb or weight in pounds.
Eventually meaning changed to becoming simply a way to denote numbers e.g #1, #2, #3. Then in #1960s Bell Labs took it, called it the #octothorpe and stuck it on phone keypads.
In early #1910s the term hash started being used for #military stripes on #uniforms but in #1980s the name hash started being assocaited with the #octothorpe symbol. From there were into modern history and early days of the internet.
In terms of social media the hash symbol + characters is a way of tagging content so a hash tag. hashtag being a shorter version is also easier programatically to identify in content.
So #hashtag is not the symbol alone. It's the symbol + the word. We went WW1 to 80s. 80s to IT/tech. IT/tech to social networking. Tada!
Now, most important thing is that there is no #algorithm on #Mastodon so people won't find your petition posts without them.
Stick a # in front of #petition and they just might!
Give it a try it's super easy and most Mastodon clients will autocomplete them for you too. 