PHILADELPHIA (CBS) – See the Liberty Bell. Eat a cheesesteak. Run up the ‘Rocky’ Steps.

They’re things on most must-do lists for tourists in Philadelphia — but police are warning of a scam ensnaring some visitors who want a photo at the city’s top sites, including that bronze Balboa statue.

At first, it might seem like a kind gesture: someone offers to take a picture of you at the attraction. But police say the offer might come with strings attached — while that person still has your smartphone in their clutches.

“Often, we have heard reports of people lurking around, waiting for those opportunities,” says police Lt. John Stanford. “Waiting to take a cell picture and asking for money as an exchange for taking a photograph — that’s not allowed.”

The warning from police comes ahead of the summer tourist season — and leading up to the Democratic National Convention in Philadelphia in July, when tens of thousands of people will descend on the city.

But when KYW reporters climbed the Art Museum steps in April, we were approached several times by men who offered to snap a picture in exchange for cash. This same kind of solicitation is mentioned on sites like Yelp and Trip Advisor.

“That is absolutely not allowed to happen in this city,” Stanford says.

To be sure, the phenomenon is not exclusive to Philadelphia; authorities in every city tell tourists to remain vigilant.

While police patrol tourist hot-spots like the Rocky Statue, you might want to play it safe — and stick to selfies.

“We have a number of bike officers that are out in that location, and we are mindful of having a police presence in that area,” Stanford explains. “We look forward to anyone visiting our city, but just be cautious and be smart.”