You asked about Germany, but maybe you also want to know how those signs are called in Austria, where people speak German too.
The Austrian StVO (StraßenVerkehrsOrdnung = road traffic act) would call the sign where you can read »Jihlava« a »Vorwegweiser«. This is how a Vorwegweiser really looks like in Austria:
And this is the version you can find in Germany:
The sign where you can read »Miami« would be a »Überkopfwegweiser«.
Example for a real Austrian Überkopfwegweiser:
Sorry, I don't know how a Überkopfwegweiser is called in Germany. Obviousely it is not »Überkopfwegweiser«, because I couldn't find a picture of a German Überkopfwegweiser.
The generic term for those signs is »Wegweiser«. (Not only in Austria, but everywhere where you speak German)
- German noun »der Weg« = »way« in English.
- German verb »weisen« = »to point, guide, show« in English.
So the literal translation of »Wegweiser« is »way-pointer«.
Other literal translations:
- Vorwegweiser = pre-way-pointer
- Überkopfwegweiser = overhead-way-pointer
Usage of »Wegweiser« in a sentence:
Look, there is direction sign, now we should turn left to continue going to Paris.
Schau, da ist ein Wegweiser, jetzt sollten wir links abbiegen um weiter nach Paris zu fahren.