Yes, in the early years there was more variety of the fonts, there were several makers. But this is not the main point.

This plate was issued in July 1956 - and not in the county Steinfurt, which you would expect, when you see a ST-plate.

It was in Stade near Hamburg. The ST-plates there were a kind of mistake, they were only issued for roundabout 600 vehicles and only for 5 weeks, then it was stopped and changed to STD.
In the 50ies West Germany believed in a the coming reunification - in the lines of 1937. And ST was reserved for Stettin (Szczecin). So Stade was stopped. In 1975 the political landscape has changed, so noone complained about the ST for Steinfurt (former BF).

I see that the font looks different on the rusty 'ST' plates. When were they issued?

For example with this:

http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=310139010006&ssPageName=ADME:X- :AAQ:DE:1123

It's something for insiders, but I know, that the real insiders are very close to a heart attack.
The plate I'm offering (the RS) is totally negligible. A bit older, but at least worthless. The decoration of the background is the real thing. There you can see the definite "holy grail" for collectors, the coelacanth for decades, very surely the one and only existing item worldwide.
All of the background stuff are nice collectibles, too, of which you know, that other collectors don't have it, but the "grail" is the rusty pair with "ST".
I wrote something about plates, which I have photographed totally randomly without recognizing the rarity (this I've seen one day later by watching the photos) - here they are. It was a long and hard work, but yesterday I could get them.

Oh, and how have heard from my friends (only three others were privy in it), I've also paid the highest known price for German plates ever.
I will not keep them, I will give them to my friends - definetely noone of the guys, who are watching that auction and will be mad for them (the first six questions I still got) will ever have the chance to get them. I just took this auction as a vehicle to show, that these precious items are existing.