For instance, posters promoting 'The Mummy: Tomb of the Dragon Emperor', which stars Brendan Fraser and Maria Bello, do not carry the film's 12A certificate - which means that under-12s can only watch if accompanied by an adult - or the BBFC's warning that it contains moderate violence and horror.
Also, studios including Universal, 20th Century Fox and Pathe are failing to include details of the explicit content of films or their age classification on posters and publicity material.
The British Board of Film Classification (BBFC) has sent a warning to the studios reminding them of their obligation.
Its guidelines require that all films which carry the U, PG, 12A, 15 and 18 certificates must display their classification and warnings about sexual or violent content on all promotional material, including trailers.
But inquiries by the BBFC and The Sunday Telegraph have found several new releases being advertised on billboards and in magazines either without their certificate or the warnings, or both.
John Beyer, the director of Mediawatch UK, said that the BBFC should do more to ensure film companies include the certificates and guidance on material.
"It is the board's responsibility placed on it by the Government to provide information for people, mainly parents with young children," Telegraph quoted him, as saying.
"I think part of the problem is that the BBFC is an industry body rather than a public body," he added.
Although the studios are not legally obliged to abide by the guidelines, the board "expects" them to do so.