I would not call it unsigned, it’s just that you have to know which local symbol to follow for the E-route. If the association of E-symbol with the local symbol is found on the ground at the beginning of a section, and preferably more points along the route, then it’s fine with me. If it’s purely external information from a web site or a printed guide, or just that everybody knows it, I would not map it, but if someone else maps it I wouldn’t delete it either. I am much stricter about copyright if the info is taken from a different source.
The association of the symbols is recorded in OSM by the local route relation being a member of the E-route relation.