[Tagging] Overhead signs (Überkopfwegweiser)

[fly]

Well, we already have two systems which work well together to get all
tagged.

1. the already mentioned destination*:lanes=* system
2. additionally the relation type=destination_sign

So the only thing I would miss are some tags to better tag the
properties of the sign itself like direction=*, support=* or ele=*.

Do we have traffic_sign=destination_sign or highway=destination_sign or
similar tag as main tag for the node.

Is gauntry that important, that we need an own main tag dor it or would
it better fit as subtag ? Eventually even support=* alone will work.

cu fly