Index: resources/data/validator/highway.mapcss
===================================================================
--- resources/data/validator/highway.mapcss	(revision 17912)
+++ resources/data/validator/highway.mapcss	(working copy)
@@ -38,6 +38,14 @@
   assertNoMatch: "node highway=turning_circle";
 }
 
+/* 17607 warn about traffic signals on roundabouts */
+way[highway][junction=roundabout] > node[highway=traffic_signals][traffic_signals=signal],
+way[highway][junction=roundabout] > node[highway][highway=~/^(traffic_signals|stop|give_way)$/][!traffic_signals] {
+  throwWarning: tr("{0} on a road with {1}", "{0.tag}", "junction=roundabout");
+  group: tr("suspicious tag combination");
+  suggestAlternative: "junction=circular"
+}
+
 way[highway=crossing],
 way[railway=crossing],
 way[railway=level_crossing] {