Shared with Poland and Switzerland
I know it must sound odd but Germany has the greatest number of divided citied in the world. The cities shared with Switzerland (Laufenburg and Rheinfelden) were divided due a treaty signed with Napoleon that the Rhine would become the border. Similarly the cities shared with Poland (several, including Goerlitz and Frankfurt an der Oder) are a consequence of the Soviet ruling that the Neisse would become the border. In both cases historical towns became split, something that affected their urban development and maintenance since. It is a phenomenon mostly prevalent in Europe and quite rare outside it.

This is quite an interesting idea though I don't think there is anything particularly tangible about the division. And also these divisions are not necessarily that permanent.
I don't think they would particularly make a great WHS but may be interesting places to visit to see the differences on different parts of the cities.

IS their a major difference between the two halves of Berlin? it might be something to consider

I think there still is.