Hi dikkeknodel

In Switzerland the E4 is signposted, but quite sparsely. Opposed to the national hiking routes that are marked with their number on every signpost, E4 signs can be found only on "main signposts" as an additional sign. The signs seem a bit dated, and I assume that they aren't maintained seriously anymore. But still, they are there. So from my point of view the information is verifiable, but for verifying, you need to find those selected spots. I've seen these signs e.g. on the town centre signposts of Rorbas, Andelfingen, and Truttikon, and at the "Herenbänkli" (Irchelturm) singpost. These signs read "Europäischer Fernwanderweg 4 Pyrenäen - Jura - Neusiedlersee". I made pictures of them when I mapped the Diesldorf to Stein am Rhein section 8 years ago. See e.g. [1].

Was it really me that started this relation? I thought it was just the Diesldorf to Stein am Rhein section. Anyway, my source of information for the St. Cergute to Dielsdorf part is/would be local knowledge and knowledge about the Swiss hiking network: I know that regional and national hiking routes in Switzerland are all based on the local waymarked trails. And that international hiking routes mostly follow the national hiking routes. And e.g. [2] confirms that "[der Jurahöhenweg] bleibt bis zum Verlassen der Schweiz der Begleiter des E4".
My source of information for the Dielsdorf to Stein am Rhein part was that same web page [2] for knowing about the rough directions. Then I went out there with my bike and followed the yellow singposts. Here again, my local knowledege and my knowledge about how the Swiss hiking network works helped me find the right path.
An example: So I knew from [2] that E4 leads from Bülach to Dorf. Looking at any hiking map, I could guess which paths I had to follow. So I went there, cycled along those paths, and in Rorbas town centre and at "Herenbänkli" (Irchelturm) I found the signs mentioned above. So I got confirmation that I was on the right path.

Here you have it. Hope that my procedure was compliant with the OSM rules.

Cheers,
schmandr

[1] https://drive.google.com/file/d/1jGuYdnnZnPTh6Mi9CHBs-W93e3x5i-cQ/view?usp=sharing
[2] https://www.outdoorseiten.net/wiki/E4#Schweiz
and a few web pages like https://www.outdoorseiten.net/wiki/E4#Schweiz and