When work by the street artist Banksy started selling for hundreds of thousands of dollars, big rectangular holes began appearing in the walls where his art used to be. This isn’t unique to Banksy. Street art theft has become relatively common because the work is vulnerable and potentially worth a lot of money.

Last week, a local photographer reported “two guys in their mid-20s with putty knives” attempting to “pry up” Toynbee tiles in Center City. Their apparent goal was to sell the tiles.

Toynbee tiles are linoleum mosaics found embedded in city streets in North and South America. They’ve appeared in crosswalks, parking lots, exit ramps, rest areas and in the middle of highways since the early 1980s. They’re the creation of an anonymous Philadelphian and bear a message calling for the physical resurrection of all human life on Jupiter. However you take the message, the tiles are appropriately regarded as works of art and the tiler as this art medium’s creator. His technique has been copied by street artists around the world.

In 2011, I was a subject and researcher for Resurrect Dead, a documentary that examined the mystery of the tiles. With unexpected success and a wide distribution, the movie has reached the point where art thieves of the world have taken notice.

Of these thieves, the Philadelphia duo has been spotted at least three times. In St. Louis, a security guard witnessed a man removing a 15-20 year old tile from the corner of Sixth and Olive streets. When asked what he was doing, he reportedly told the guard that “it was going to be worth a lot of money.” That tile is now gone.

If left undisturbed, Toynbee tiles can last as long as the asphalt. The tile fragment in the photo at the top of this article, at Ninth and Locust Streets was recently revealed by the erosion of crosswalk paint. It’s 20-30 years old.

A tile at Fourth and South Streets survived in good condition from the early-1990s until road resurfacing in December, 2008.

When well set, tiles sit flush with the asphalt and are extremely hard to remove. The Philly thieves aren’t using heavy duty tools and from what I can tell, they’ve been relatively unsuccessful in removing them. One small tile from around 2004 was pried from the northwest corner of Juniper and Chestnut.

Of course, whatever their value is as art or as a commodity, all the tiles are ultimately doomed. As durable a material as it is, Linoleum erodes and streets are fairly often repaved. At least a dozen tiles were destroyed by routine roadwork in the past couple of weeks. Whatever the intention of the thieves, at some level they’re doing a service in preserving the physical artifact. In no way do I condone what they’re doing, but it’s instructive to acknowledge the accidental benefit that may come from it.

While most street art is meant to be temporary, and the question of preservation essentially contradictory to the work’s original intent, the tiles are different. I can’t speak for the creator, but have a pretty good idea that the message and the idea presented trumps the art. We do know that tiles were embedded in the street to make them as public and permanent as possible–tiling was a direct reaction to the impermanence of paper signs.

With that said, thievery isn’t the only way to preserve these unique pieces of art. Why not carve them out, secure them, protect them and display them publicly? I envision a series of Toynbee Idea lightbox displays, preserved tiles inside, attached to street lampposts, buildings, and bus shelters around town. At the very least, an interested museum or preservation body can work with the Streets Department to save a small collection of tiles before scheduled street repairs.

Why save them? Perhaps for no other reason than their perceived value in the art market. I’m eager to work with any organization or group interested in preserving this odd aspect of Philadelphia culture and history.