The US federal government has mandated the use of several standard typefaces (or "Alphabet"s in their terminology) which must be used on road signs. Collectively, they are the Standard Alphabets for Traffic Control Devices, or SAFTCD, and are colloquially known as "Highway Gothic". Unfortunately, there are only really two implementations of the full set of type faces: there is a "roadgeek" set which is free for noncommercial use and there is a set which costs around $800.
This project seeks to provide an implementation of all currently-documented SAFTCD typefaces placed in the Creative Commons. They are free for all uses, and may be freely modified, so long as my original copyright message stays in the font info.
If you want a road sign font, you can pay $800 (for the full set) or you can make your own. You also have several other options like Blue Highway or the roadgeek fonts, although the latter is often criticized for being poorly put together (badly authored.) The creator of that set simply traced the existing fonts. I have no idea why, because you can download the "Manual on Uniform Traffic Control Devices" which contains all the outlines.
sIFR is a tool that replaces text elements in a webpage with some styled flash text. While there are some failings in the tool (currently version 2.0.2, with version 3 now in alpha testing) it is in general the only highly-supported way to use nonstandard fonts in webpages.
I have taken the time and effort to finally make sIFR work on this site; I tried it out a long time ago but ended up being confused. Actually, I'm still confused; when you replace elements, sometimes elements you have no interest in seem to be replaced, even though the generated source (not the original page source, but what's actually rendered) doesn't show any way that the styles should match those elements. I was forced to use more restrictive CSS in the sIFR style sheet than I liked, but it's working out okay so far.
Seagate, the world-renowned hard drive manufacturer and the first one to bring back five year warranties across their product line, still uses text documents to provide you drive specs and jumper settings. These documents utilize the IBM PC graphics characters, which have been disappearing from fonts in recent years in favor of international characters and the like. In a more technical sense, it's the proliferation of ISO-Latin-1 over IBM-PC-Graphics.