Updated: 2012-01-18 08:33

By Wang Hongyi (chinadaily.com.cn)

SHANGHAI – That strange mark outside your door may mean nothing to you, but it could mean a lot to a thief who is thinking of breaking in.

“Thieves often conduct reconnaissance on a target household for a long time before attempting to break in,” said Tong Jianghua, 51, a police officer at Jiangdong branch of Ningbo public security bureau in Zhejiang province.

“And some thieves will leave special marks at the entrances of buildings or houses which they intend to break into.”

Since many of these marks are only understood by thieves, Tong released the list on his micro blog at weibo.com earlier this month.

A pentagram, for instance, signifies a target chosen for break-in, a letter D means the household is dangerous and not worth the attempt, and a circle means the bad guy believes there is a considerable amount of money in a household.

“This is actually a revised version of symbols used by thieves,” Tong told China Daily.

Symbols previously published on the Internet were misunderstood by netizens, so Tang has revised the chart based on his 28 years in criminal investigation.

He noted that these marks are not fixed or unified, as groups of thieves may establish different marks of their own.

“What residents should do is to enhance their alertness and contact police if they see strange marks near their doors,” he said.

Tong said police have been aware of these symbols for years.

“We received reports of these strange symbols by local residents as early as 2008, and such symbols have been prevalent among thieves,” he said.

According to an official from the Shanghai public security bureau who did not want to be identified, the number of reported thefts and burglaries before the Spring Festival usually increases about 20 percent.

In addition to the symbols, Tong also gave some tips on how to avoid losses from thieves.

For example, residents could turn on a light when going out for a short time, creating an impression that someone is home.

“Some people are used to leaving a lot cash at home, which is not safe,” Tong said, noting residents should save valuables in the bank.

“This chart is a very good reminder as we often overlook these ordinary marks on the wall,” said a Shanghai woman surnamed Jin.

“Although thieves may change their symbols, it reminds everyone to raise their vigilance,” she said.