To all of my well-intentioned relatives:
An Urban Legend is basically just a story. It's a piece of fiction that never actually happened. Most urban legends on the internet take the form of warnings against fake crime sprees (gangs using baby seats, chloroform in perfume samples), fake food scares (HIV in pepsi, PCP in lollipops) and fake celebrity news. They have sometimes been used to spread computer viruses and sometimes sent as a trick just to fool people, but are most often forwarded in good faith by people who don't realise that they are taking part in a hoax and passing on false information.
Snopes.com is a very good website that lists all of the Urban Legends that they have found on the internet, and will helpfully tell you which ones are true, and which ones are completely made up.
The easiest way to spot an urban legend is if you receive an email that claims to come from any Police Service. The police have a very good relationship with the press and the media, and any police service that needs to inform you about a crime spree or dangerous scam will always inform the local newspaper and the local television station. They almost never email people individually about crimes, because they can tell you all at once on the six o'clock news. If you get an email about a horrible crime that hasn't been on the six o'clock news, always be suspicious.
There are lots of crimes that don't get reported in the news, usually those crimes that happen to poor young men of colour. The media in this country have an overwhelming bias towards reporting crimes that have happened to pretty young white women. If your email is warning about a spate of violent attacks on young women that haven't been mentioned in a single tabloid newspaper, it's definitely a fake.
Another good way to tell is if a lot of the email is in BIG BLOCK CAPITALS. URBAN LEGENDS LOVE CAPITAL LETTERS. And it's a dead giveaway, because every private office and every police service has the same policy against using CAPITAL LETTERS in any official document. It's unprofessional, and is considered to be THREATENING LANGUAGE. So if someone left THE CAPS LOCK ON FOR THE SCARY PART OF THE MESSAGE, you have an urban legend, not a police press release.
The 'safety advice' given in most urban legends is extremely inaccurate and misleading, especially as the risks they warn you about have never actually happened! If you see someone driving with their headlights turned off, you should always flash to let them know, otherwise they are likely to cause an accident. No-one has ever been murdered for flashing their headlights, but plenty of people have crashed into cars with no lights on.
If you see an occupied baby-seat abandoned by the side of the road you should always stop to help. No-one has ever been raped or robbed by stopping to help a poor abandoned baby, and sadly babies do get abandoned from time to time. Of course be very careful of the real danger of stopping by the side of the road, which is the extremely high risk of you and the poor baby being hit by a passing car.
The worst thing about most Urban Legends is the horrible attitudes they display. A lot of them seem to take the theme of "Women, know your limits!" and insist that any girl outside of the house doing anything as simple as shopping or driving is in terrible danger of being attacked, raped and murdered. While undoubtedly these things do happen to a tiny minority of women, the sad fact is that most rapes are carried out by people that the victim already knows, and most murdered women are killed by their husbands, lovers or exes. If your other half doesn't appear to be the murdering type, you're most likely safer than you think.
And of course, the 'Gangs' mentioned in these legends (which are always enormously racist against poor young men of colour) have much better things to do than trawling the streets looking for random people to murder. The tiny minority of genuine criminals are kept much too busy with drug empires and turf wars, and usually have a long list of rivals to murder before they'd ever consider killing anyone for flashing their headlights. So while there are bad people in the world, you really don't have to be afraid to drive at night. Unless you forget your headlights.