The council has teamed up with anti-litter campaigners to urge visitors to the seafront and green spaces not to dump their rubbish.
The goal is to make sure rubbish is disposed of properly, so it doesn't litter local beauty spots such as Southsea Common, parks and the seafront, and endanger wildlife.
Campaigners led by Plastic Free Portsmouth have produced posters reminding people to either bin their trash or take it home, with the slogan 'Proud of Portsmouth'.
The council has paid for 120 posters to be printed. Most will go in local shop windows and near takeaway food outlets, while others will be displayed on council poster sites.
Residents can join in the campaign by downloading them at plasticfreeportsmouth.wordpress.com
The anti-litter campaign also involves Just One Ocean, Portsmouth Music Hub, local businesses and artists and Southsea Beachwatch.
Cllr Steve Pitt, Deputy Leader of the Council, said: "Plastic Free Portsmouth are doing a great job of reminding us all that we need to look after our city by not leaving litter behind. As well as being unsightly, it can damage the environment and hurt wildlife. And of course, it costs public money when we have to clear it up.
"We're very happy to contribute to this campaign and help spread the word."
Southsea resident Clare Seek, of Plastic Free Portsmouth, said: "We want people to go to the Common and our other open spaces and have a good time, and then leave them as they'd like to find them.
"It's just remembering to use a bin, or ideally take your litter home and recycle it if you can. We're hoping the posters will nudge people to make little changes that make a difference.
"Last year it cost more than £22,000 of our city's money to clear up the Common alone. It would be great if that could be spent elsewhere.
"Let's all have a great summer and make sure the environment has a great time too."