When the Democratic National Convention comes to town this month - bringing tens of thousands of protesters with it - Sgt. Eric Gripp likely will be somewhere in the throng, equipped with two cellphones, four batteries, and a very influential Twitter account.

The voice of the Philadelphia Police Department's social-media presence is best known, by day, for his meme-filled posts on the department's Facebook and Twitter pages.

But Gripp, 35, also has been an enduring presence at some of the biggest protests the city has seen in recent years, including last year's Black Lives Matter demonstrations, and he's well aware that what he tweets goes a long way.

"You're not just the voice of yourself," he said. "You're the voice of the department."

As the voice of his department, Gripp can be snarky, self-deprecating, and, occasionally, deeply and unabashedly weird. He has repurposed Kanye West tweets and vintage TV commercials into recruitment ads for the police. He once Photoshopped a jetpack onto then-Commissioner Charles H. Ramsey for an April Fool's Day post.

And he tries to balance it all - delicately - with the realities of crime in a major city, posting daily bulletins on unsolved crimes and arrest updates in between less urgent tweets and posts.

Police departments are just beginning to grasp how they can use social media, said Lori Brainerd, a public policy professor at George Washington University who researches how those departments interact with the public online.

"There are no best practices, and so we are making this up as we go along," she said. "In some senses, that's really good - you have these real, live experiments going on. But the stakes are really high when it involves something like protests, or the DNC."

Police can build trust through tweeting, Brainerd said - or make protesters feel spied-upon. And there is little room for error.

"You're creating a public record in real time," she said. "Anything you say is now magnified for millions of people."

This has worked to some departments' detriment.

Amid chaotic protests and rioting after Freddie Gray's death in police custody in Baltimore last year, police there live-tweeted the scene. "Officers are now deploying pepper balls at the aggressive crowd," the department wrote on Twitter.

Later: "A group of criminals have just started a fire outside the library located at Pennsylvania Ave and North Ave." Those following the events on Twitter sent dozens of tweets arguing over the department's tone.

Philadelphia has not been rocked with the kind of large-scale protests that cities like Baltimore and Ferguson, Mo., have seen. Last spring's Black Lives Matter protests here were largely peaceful if occasionally unruly. "The peaceful protest stops at 15th and Locust to express their 1st amendment rights," Gripp wrote from the scene of one march.

The sergeant's strategy at such events boils down to "just being honest," he said. "If the protest is moving, we say it's moving. If it's peaceful, we say it's peaceful."

Gripp got the social-media gig in 2013, after six years serving in the 22nd District, one of the city's most crime-ridden.

On the side, he played in a cover band called Huge Jackman - and, naturally, had taken over its social-media presence. Lt. John Stanford, another 22nd District veteran and now the department's chief spokesman, noticed Gripp's knack for social media.

"I told him how lacking our social media was," Gripp said. "We want to be where people are - not to watch anybody, but to be there in case anybody tries to contact us."

Recently, the department opened a Snapchat account.

"We're still trying to figure out where to use it," Gripp said, laughing. So far, he has fielded about "five actual questions" via the photo- and video-sharing app. The rest? "Lots of things I'd like to un-see," he demurred.

For the Democratic convention July 25 to 28, with the promise of protesters pouring through the streets, Gripp's plan is simple: "Be honest. Answer as many questions as we can." The papal visit in September was valuable training for the more volatile DNC atmosphere, he said - from verifying crowd reports to responding to requests for help.

"We're going to be prepared and protecting everyone's constitutional rights," Gripp said.

Some of those who have dealt with the department for decades view such language with caution. Noted civil rights lawyer David Rudovsky said he's encouraged by Mayor Kenney and Commissioner Richard Ross' insistence that protesters' rights be protected during the convention. But he also recalls similar promises during the 2000 Republican convention, when hundreds of protesters were arrested on charges that were later tossed out.

"Their statements as to policy are very important in terms of community relations, but only if you follow through," Rudovsky said.

Policy decisions are above Gripp's rank. At the convention, the voice of the department will simply try to call it as he sees it - online and on the ground.

"We want to make sure we're everywhere where people might want to reach us," Gripp said. "If problems start to happen on the street, we'll see them."

awhelan@philly.com

215-854-2961 @aubreyjwhelan