diff --git a/pkg/server/sig.go b/pkg/server/sig.go
index 322dd8ae9..feb88b2f9 100644
--- a/pkg/server/sig.go
+++ b/pkg/server/sig.go
@@ -132,6 +132,19 @@ func (h *JSONSignHandler) uploadPublicKey(sto blobserver.Storage, key string) er
 	return err
 }
 
+func (h *JSONSignHandler) discoveryMap(base string) map[string]interface{} {
+	m := map[string]interface{}{
+		"publicKeyId":   h.entity.PrimaryKey.KeyIdString(),
+		"signHandler":   base + "camli/sig/sign",
+		"verifyHandler": base + "camli/sig/verify",
+	}
+	if h.pubKeyBlobRef != nil {
+		m["publicKeyBlobRef"] = h.pubKeyBlobRef.String()
+		m["publicKey"] = base + h.pubKeyBlobRefServeSuffix
+	}
+	return m
+}
+
 func (h *JSONSignHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 	base := req.Header.Get("X-PrefixHandler-PathBase")
 	subPath := req.Header.Get("X-PrefixHandler-PathSuffix")
@@ -150,16 +163,7 @@ func (h *JSONSignHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 			http.Error(rw, "POST required", 400)
 			return
 		case "camli/sig/discovery":
-			m := map[string]interface{}{
-				"publicKeyId":   h.entity.PrimaryKey.KeyIdString(),
-				"signHandler":   base + "camli/sig/sign",
-				"verifyHandler": base + "camli/sig/verify",
-			}
-			if h.pubKeyBlobRef != nil {
-				m["publicKeyBlobRef"] = h.pubKeyBlobRef.String()
-				m["publicKey"] = base + h.pubKeyBlobRefServeSuffix
-			}
-			httputil.ReturnJSON(rw, m)
+			httputil.ReturnJSON(rw, h.discoveryMap(base))
 			return
 		}
 	case "POST":
diff --git a/pkg/server/ui.go b/pkg/server/ui.go
index 23b8f4590..2d135daf1 100644
--- a/pkg/server/ui.go
+++ b/pkg/server/ui.go
@@ -77,6 +77,7 @@ type UIHandler struct {
 
 	prefix string // of the UI handler itself
 	root   *RootHandler
+	sigh   *JSONSignHandler // or nil
 
 	Cache blobserver.Storage // or nil
 	sc    ScaledImage        // cache for scaled images, optional
@@ -101,6 +102,13 @@ func newUIFromConfig(ld blobserver.Loader, conf jsonconfig.Obj) (h http.Handler,
 		return
 	}
 
+	if ui.JSONSignRoot != "" {
+		h, _ := ld.GetHandler(ui.JSONSignRoot)
+		if sigh, ok := h.(*JSONSignHandler); ok {
+			ui.sigh = sigh
+		}
+	}
+
 	ui.PublishRoots = make(map[string]*PublishHandler)
 	for _, pubRoot := range pubRoots {
 		h, err := ld.GetHandler(pubRoot)
@@ -295,6 +303,9 @@ func (ui *UIHandler) populateDiscoveryMap(m map[string]interface{}) {
 		"directoryHelper": path.Join(ui.prefix, "tree") + "/",
 		"publishRoots":    pubRoots,
 	}
+	if ui.sigh != nil {
+		uiDisco["signing"] = ui.sigh.discoveryMap(ui.JSONSignRoot)
+	}
 	for k, v := range uiDisco {
 		if _, ok := m[k]; ok {
 			log.Fatalf("Duplicate discovery key %q", k)