Use error message !! hints (#16145)

Marlin/src/core/language.h

@@ -252,10 +252,10 @@
 #define MSG_FILAMENT_CHANGE_INSERT_M108     "Insert filament and send M108"
 #define MSG_FILAMENT_CHANGE_WAIT_M108       "Send M108 to resume"
 
-#define MSG_STOP_BLTOUCH                    "STOP called because of BLTouch error - restart with M999"
-#define MSG_STOP_UNHOMED                    "STOP called because of unhomed error - restart with M999"
-#define MSG_KILL_INACTIVE_TIME              "KILL caused by too much inactive time - current command: "
-#define MSG_KILL_BUTTON                     "KILL caused by KILL button/pin"
+#define MSG_STOP_BLTOUCH                    "!! STOP called because of BLTouch error - restart with M999"
+#define MSG_STOP_UNHOMED                    "!! STOP called because of unhomed error - restart with M999"
+#define MSG_KILL_INACTIVE_TIME              "!! KILL caused by too much inactive time - current command: "
+#define MSG_KILL_BUTTON                     "!! KILL caused by KILL button/pin"
 
 // temperature.cpp strings
 #define MSG_PID_AUTOTUNE_PREFIX             "PID Autotune"