If you want to add the relation, the easiest way is to take a georeferenced photo of each signpost. After that you can put the ways between the signposts in the relation.

If you don't know how to manage relations, you can also make photos, for example with "mapillary", which then can be used by other mappers to add the bicycle route. 

Another option to exchange photos is the app "StreetComplete", which allows you to create notes and attach photos to them. If you create a note of every signpost, with one photo from a few steps away so others know the direction of the routes, and one photo from the text (or  markers), to know the name or the icon of the route, it shouldn't be that hard to add the relation remotely without local knowledge.

(If you want you can also write in german language, but if you're english, that's no problem. Normally the language of osm changeset-comments and notes should be in the country's language, or in English).