Iron railroad spikes are a quintessential hoodoo tool/curio, prized for their symbology of protection and warding. I have heard people using them to protect their homes by taking 4 of the spikes and burying them in the four corners of their house to "stake down" their home. 
 
Personally, I like to keep one in my car (and have given one to my father to keep in his car as he is on the road a lot). 
 
They are also spectacular offerings to leave (ironically) at the crossroads, if you are working with spirits that meet there.
 
Additionally I feel that the railroad spikes resonate with the ancestors as they also represent support, history, and relying on our roots. 
 
Hand collected by the Moth Queen. (I will upload a better picture later)