specify icons for crossing markings

data/fields/crossing/markings.json

@@ -20,5 +20,19 @@
             "zebra:bicolour": "Longitudinal Bars With Alternating Colors",
             "ladder:paired": "Ladder With Paired Longitudinal Bars"
         }
+    },
+    "icons": {
+        "zebra": "iD-crossing_markings-zebra",
+        "lines": "iD-crossing_markings-lines",
+        "ladder": "iD-crossing_markings-ladder",
+        "dots": "iD-crossing_markings-dots",
+        "dashes": "iD-crossing_markings-dashes",
+        "surface": "iD-crossing_markings-surface",
+        "ladder:skewed": "iD-crossing_markings-ladder_skewed",
+        "lines:paired": "iD-crossing_markings-lines_paired",
+        "zebra:double": "iD-crossing_markings-zebra_double",
+        "zebra:paired": "iD-crossing_markings-zebra_paired",
+        "zebra:bicolour": "iD-crossing_markings-zebra_bicolour",
+        "ladder:paired": "iD-crossing_markings-ladder_paired"
     }
 }

data/fields/crossing/markings_yes.json

@@ -3,5 +3,6 @@
     "type": "combo",
     "label": "{crossing/markings}",
     "stringsCrossReference": "{crossing/markings}",
+    "iconsCrossReference": "{crossing/markings}",
     "default": "yes"
 }