Yep, as others have noted, the Green Sign = Trunk Road is the age old convention. If you want to add details about who maintains the road you can use operator=Highways_Agency (the second highest use of the operator tag apparently [1]). We don't have a tag for indicating that the signs are green (hence it would be nice if people stick to the convention).
Regards, Rob [1] http://taginfo.openstreetmap.org/keys/operator#values
_______________________________________________ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
