"Ishiyaki Imo" means baked sweet potato which the roasted gravel in English.

It is almost always sold in the food stand, not in stores. Most stands use a light truck.
The Goods and cooking equipment are carried in the back of truck.
The vender announces his presence by chanting "ya-ki imo...ishiyakiimo", often with a repeating tape recording.
The residents must come running when they hear him. Because the truck is moving although only slowly.

"Ishiyaki Imo" begins to be sold near the end of the autumn. Japanese feel the visit of the winter when they hear the announce of "Ya~ki imo~".