Part of a now defunct fan project, these were available to purchase for a short while. All profits from them were and will be donated to Toys For Tots.
"What's that? Speak up boy! Cyberponies on Castrovalva, you say? Well, all good things must come to a bend. Come along Miss Hooves, pack up the Jelly Babies and Allons-y!"
Let me start by saying that I am several kinds of nerd. One of which is a massive Doctor Who nerd, I've actually seen almost all of every series, from the 1st all the way up to the 11th. Well, I skipped most of Colin Baker, but I think that's excusable. The 6th Doctor kinda sucked.
So on that note, when this spiky maned background pony with the hourglass cutie mark began to appear on the show, it didn't take long for people to notice his striking resemblance to the tenth Doctor, David Tennant. I dunno if some animator is just a sly Doctor Who fan or what, but the fans took to it. The shoe was a blast to design. The traditional side body color and cutie mark are there, but the tongue has a stylized image of the TARDIS doors, and the heel shows a larger image of the police star on the door. It's based off the first Doctor's TARDIS, but I guess also the current, since they went with a classic TARDIS exterior. By far my favorite shoe, since I'm such a fanboy for these kinds of things. I actually saved up and got a pair of these myself.
Fun fact, the item description up there contains references to five specific Doctors. Kudos to the first person to guess them correctly.