Yesterday we reported on how Reddit’s people power led to some significant changes on one of the site’s subforums.

But now redditors in another popular subreddit have begun agitating for a very real, offline cause: marijuana legalization.

Yesterday redditor almantimes2 posted a link in the site’s marijuana subreddit to an online petition created by a pro-legalization organization called NORML.

The petition aims to show public support for the recent bill proposed by representatives Barney Frank and Ron Paul that would decriminalize marijuana at the federal level.

“This is definitely historical legislation,” almantimes2 wrote. “We need all the help we can get.”

Since then, the subreddit, which has over 90,000 subscribers, has helped the petition reach over 13,000 signatures.

So what will those signatures do?

“Nothing,” said Allen St. Pierre, executive director of NORML.

It’s not a legally binding petition and as such has little real-world political weight, St. Pierre said.

But that doesn’t make the campaign unimportant. What online petitions like this do — and the reason NORML organizes them — is create demonstrable momentum behind a movement.

Or to put it another way, they build buzz — something that would have been impossible 20 years ago. In the past the mainstream media cut down the legalization agenda “at the knees,” St. Pierre said.

Now, aggregation sites like Reddit decide for themselves what’s newsorthy.

“Bigger aggregators are almost always near the top of our referral service when we put out small but Internet friendly projects,” St. Pierre said.

And what’s more, mobilizing people to a similar degree just 20 years ago would have cost the organization tens of thousands of dollars.

“It would have put us in bankruptcy,” St. Pierre said.

For NORML’s communication director, Erik Altieri, that makes getting the word out much easier. All he needed to do was post the petition to NORML’s Twitter and Facebook pages and then watch it spread.

“The Reddit community just seems to have taken it up on their own,” Altieri said.

“This whole campaign is really a shining example of the power that lies in the viral nature of the Internet and social media,” he added.

So while signatures on a petition do not necessarily equal votes in congress, they do “drive the discussion,” St. Pierre, the exectuive director, said.

And on Reddit, that is certainly worth an upvote. Or uptoke, if you prefer.