They were erected in the 1940s to repel unwanted visitors - but cash is now needed to help turn anti-tank defences into a tourist attraction.
Eastney Signage Campaign needs to raise 2,500 for signs to let visitors to Fraser Beach, Eastney, know more about the 280-block, 400m Grade Two listed site of special historic importance.
Treasurer David Denison said: 'The signs are needed because, at the moment, people who see the anti-tank barriers might just think they're a lot of concrete cubes just lying about. I admit when I first saw them I wasn't too impressed. But they are an historic monument and if we get the signs up, we can let people know what they're seeing.'
The blocks were laid between Eastney Fort East and Fort Cumberland, as part of the nation's defences against a potential invasion by German sea forces during the Second World War.
They were granted heritage status in March this year, which means they are protected from damage and can't be removed for development without specific government permission.
Mr Denison said: 'That was excellent news, because the monument's just five metres from where QinetiQ want to build their flats at Fraser Range. But now we want to make sure the people who come here know about them. It's another chunk of history, so we should let people know.'
The campaign is working with Portsmouth City Council to pay for two signs, one at each end of the monument, which will carry photographs as well as written information.
It has been told the signs will cost 2,500, though the group is hopeful the council will pay half that amount.
Mr Denison said: 'It's quite a lot of money, but we need to make sure the signs are hard-wearing and vandal-proof, and the council may be able to help us by match-funding. We have raised 500 so far, so we have a little way to go, but we hope we can soon have the signs to explain about the anti-tank defences.'
To make a donation, send a cheque payable to Eastney Beach Signage, to Eastney Beach Signage Campaign, PO Box 551, Portsmouth PO5 1ZN; pay direct at Nationwide, with sort code 070093, account reference 0373/704236700; or pay at another bank adding Nationwide identity account number 33333334.