修改pod 提示信息

RA Image/RA Image/PODModeViewController.m

@@ -139,7 +139,7 @@
         return;
     }
     if (self.signature == nil) {
-        [RAUtils message_alert:@"You must sign." title:@"Warning" controller:self];
+        [RAUtils message_alert:@"Signature is missing." title:@"Warning" controller:self];
         return;
     }