I believe I did find at least one of them near a railroad! Y'all never cease to amaze me. And a telephone pole tag is a good guess too considering I hunted a lot of city easements where those poles are located. Thanks again!
The ones used in railroad applications (date nails) are commonly larger than this, as they have to put up with tremendous vibration over many years. Storm window numbering tacks are smaller (like these).
window numbering tacks: http://www.smithrestorationsash.com/acrowindowtacks.html
railroad date nails: DATE NAIL INFO - note the size
Thank you oh wise ones! I never would have guessed that. Heck, I didn't even know they existed. They should change the site name to Treasurenet University. I learn something new everyday here