Read this article by Sam Roberts.
Semicolon sightings in the city are unusual, but Neil Neches, a writer in the transit agency’s marketing and service information department, inserted one on a placard anyway.
This article articulates the wonder in seeing a semicolon in such an odd place, but other grammarians, professors, and teachers are delighted to see it used properly.
The reason the semicolon is so rarely seen and used is simply because not many know how to use it properly. In the wave of technology and IM/text speak, a semicolon is used to wink at someone.
Check out the article for more information. 😉