Police departments around the country are warning about a popular scam that targets the elderly.

It goes something like this: someone knocks on your door and tells you they've painted your house number on the curb. Maybe they explain that they work for your city or town, and claim that you already owe them money for the job. If you refuse, they might get angry or threaten that you'll get in trouble.

This is one of those scams that pops up over and over again, and in a surprising number of places around the world. People from Los Angeles to Australia have reported being harassed by number painters looking to make a quick buck.

Police want you to know that if you didn't ask for any work to be done around your house, you have no obligation to pay anyone for their work. If you think you're being scammed, or if the number painter is acting abusive towards you, record a description of them and their vehicle and call the non-emergency number for your local police department.

To make things even more confusing, some towns will pay number painters to draw your house number on the curb. This has lead to some ugly confrontations between city workers and home owners who think they're being scammed.

But there are some clues that can help you tell a scam artist from a real painter...

If you recognize any of these common tricks, the paint job is probably some kind of scam:

• Some painters leave notes for home owners to find which look like official notices from the city. Read them carefully and call the local works department to check if they're legitimate.
• Ask the painters for a permit. Most locations require curb painters to get a work permit from the city, even if they're working independently.
• Scam artists won't list an amount for their work to "fish" for a large amount, or will give a price that seems much too high, like $20 or $50.
• They might tell you that you have to post a notice on your door asking not to have the numbers painted, or else you're required to pay up. This isn't true.
• They might explain that they're collecting money for a charity of some kind. If that's true, you should be able to ask for a brochure or pamphlet, and ask questions about the charity.
• You can always call your local public works office to check if painters are working on your street.
• Scammers might say that your neighbors have already agreed to pay, but you should check to see if that's true.
• Check if they're driving a public works department vehicle.

Most people are happy to cough up money when scammers ask for it, but they may find the work never gets done. Other scammers will do the paint job, but then ask for more than you originally agreed to pay.

Meanwhile, some number painters are legitimate business people. Some will even add special touches like your family name or a sports team's logo on request. If the painters seem polite and honest, and they don't charge very much, it should be safe to accept their offer.

Share this warning so everyone will know about the number painting scam!