On Aug. 23, 2007 — 10 years ago today — he sent a tweet asking Twitter users what they thought about adding a pound sign before a topic like “#barcamp” — another event popular among people in the technology industry.
It was “the simplest idea that could work,” Mr. Messina, 36, a product designer from San Francisco, said in a telephone interview on Tuesday. It gave people a tool, he added, that would enable them “to participate in a powerful way on social media.”
A decade later, an average of 125 million hashtags — as those pound signs came to be known — are shared every day around the world on Twitter, the company said. Indeed, Mr. Messina had given birth to a tool that would infiltrate our vernacular, aggregate conversations and, yes, fill screens with unnecessary, meaningless garble.
Hashtags have proven most useful for filtering conversations about events exactly like South by Southwest. Take the Super Bowl, for instance, which Twitter said is the most tweeted sporting event hashtag in the United States; or consider how hashtags help you find photos from your friend’s wedding — or even let you see the best shots of a hugely hyped eclipse.
To be clear, you don’t need to use hashtags to conduct a filtering search on Twitter. And if millions of people are tweeting about a new Star Wars trailer, all at the same time, the odds that your tweet will surface and find a huge audience are minuscule.
But Robert Hernandez, a digital journalism professor at the University of Southern California, said “there is still something wonderful” about watching a community come together in real time “only because of a hashtag.”
Mr. Hernandez pointed to #yesallwomen, which allowed hundreds of thousands of strangers to discuss violence against women and reveal their anger and horror about abuse and sexism. Mr. Messina cited #blacklivesmatter as an example of a hashtag that is “powerful and necessary.”
He doesn’t think badly of people who use #waffle to label a photo of a waffle. That person is “trying to express something,” he said, and you have to take the good with the bad.
Mr. Hernandez is also a fan of hashtags; he’s a co-founder of a weekly Twitter forum about online journalism called #wjchat. But he acknowledged that they can grate and irritate.
“Like anything that becomes popular — especially if it was organic and grass roots — corporations take it over and incorporate it into marketing,” Mr. Hernandez said. People are unlikely to use hashtags created by brands, he added, no matter how much they are promoted.
He pointed out another issue too. “I’m sure there are countless hashtags that only one person has tweeted on,” he said, which creates a sort of “hashtag pollution.”
Getting a large group of people to do the extra work of adding a hashtag was hard at first, Mr. Messina said. But sometime around 2010, grass-roots organizers with the Tea Party movement began using hashtags to streamline their messages, which he credited with helping the form take off.
Some time later, Instagram took on the hashtag and gave it additional utility. Today, hashtags are used widely on the platform to label photos so that more people see — and like — them.
It’s quite the shift from the days when Mr. Messina — Twitter user #1185 — considered the possibility of what he called “tag channels” demarcated by “the hash (#) character.”
“I’m super gratified at how many people actually use it for all kinds of purposes,” said Mr. Messina. “It’s giving humanity a way to express themselves — as incoherent as it may be.”