I'm in Trinity Park, and my house was built around 1925, so I suppose there could've been horses around here not so very, very long ago?
From luckymojo.com, here's some info on horseshoe symbolism:
The use of worn-out horseshoes as magically protective amulets -- especially hung above or next to doorways -- originated in Europe, where one can still find them nailed onto houses, barns, and stables from Italy through Germany and up into Britain and Scandinavia. Additionally, wall hangings made in the form of horseshoes are common. In the Middle-East, one finds the terra cotta blue glazed horseshoe plaque. In Turkey small metal or blue glass horseshoes are blended with the protective all seeing eye to form a unique apotropaic charm i call the horseshoe-and-eyes that is believed to ward off the evil eye.