@openstreetmap/id-tagging-schema/data/fields/railway/signal/direction.json

The OpenStreetMap tagging model used by the iD editor

{
    "key": "railway:signal:direction",
    "type": "radio",
    "label": "Direction Affected",
    "strings": {
        "options": {
            "forward": "Forward",
            "backward": "Backward",
            "both": "Both / All"
        }
    },
    "autoSuggestions": false,
    "customValues": false
}