Indeed, restriction relations require the from and to members to be ways in all cases. This is appropriate because turn restrictions affect the routing graph, which is fundamentally a structure made of weighted edges. Sometimes turn restrictions result in short ways, but the same can happen in some similar situations when avoiding relations.
Note that there’s no need to begin the way at exactly the location of the sign (green in your diagram). Since there’s no driveway between the intersection and the sign, you should begin the restriction at the intersection. This might require multiple restriction relations to cover all the paths that someone might take to get to the intersection.