Yes - that is a sign that the glow plug is bad. If someone could explain why that is that would be helpful too - does the glow plug actually stay lit while driving? It seems like the glow plug should always go out after you take it off and it shouldn't need it to be lit but I must be wrong.
Here's a list of FAQ's that may help on many of these types of questions (since a lot of us buying these cars may be pretty new to nitro's in general)
http://www.genxhobbies.com/rc_car_rc...htm#glowdriver