>>2279276E4 goes through the National Blue trail in Hungary, it has stamps, an official notebook with maps and a badge if you complete it. You only have to follow one marking throughout the entire route. I'm not sure about the rest, but I heard the Austrian/German part of E4 is also easy to follow.
This guy hiked through E4, if you're interested, watch his videos:
https://www.youtube.com/watch?v=hy7qsn2tP88https://www.youtube.com/watch?v=j0C5Lg1L8F0https://www.youtube.com/watch?v=jNArav7TiLEhttps://www.youtube.com/watch?v=QspZnDjDrgYhttps://www.youtube.com/watch?v=lTOvYe8Ougchttps://www.youtube.com/watch?v=gRsq7bnclYs