The campaign is part of the Met's Operation Safer Streets, which is designed to reduce street robbery in high crime zones such as train and tube stations.
The two-week campaign, reminding Londoners to be vigilant, carries the strapline "Out of sight is safer". Operation Safer Streets is the Met's response to street crime within London and was first launched in February 2001.
The campaign will run on posters in London Underground and train stations, on trains and buses, and along high streets on sandwich boards. The drive will be supported by radio.
Assistant Commissioner Tim Godwin said: "The message is simple: keep valuables out of sight whenever possible, especially at crime hotspots like tube and train stations. When you do have to take your phone or cash out in a public place, be aware of who's around you. Street robbers tend to be opportunistic -- don't make yourself an easy target."
Since its implementation, Safer Streets, which was originally concentrated across nine boroughs before being rolled out across the capital, has had notable success in bringing down levels of street crime.
According to the Met, from around 7,000 reported offences a month in late 2001, the reported monthly crime rate has fallen to around 5,000 for most of 2002 and to date.
The Met's figures say that approximately 50% of reported street crime involves mobile phones and that 30% of street crime consists solely of the theft of a mobile.
Previous Safer Streets campaigns have included highlighting the benefits of marking property with permanent marker so that it can be returned to the rightful owner if found by police.
The Safer Streets campaign follows a recent joint advertising campaign with the mobile phone industry to tell the public that they can have a phone disabled via a central telephone reporting system, should it be stolen.
The ads were created by The Advertising Syndicate with media planning and buying through MediaCom.
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