Yes and no (sorry, but it's true). When no signal is being detected it will be off (since you're scanning and it'll stop on a desired signal this is good). When scanning a trunking system, it'll be on since it's receiving the control channel (you may not hear anything if the system is inactive or talkgroups you have locked out are the only ones active). When you're listening to a transmission, it'll show the strength of the signal you're hearing (as you expect).