The PRI flashing in the corner is only applicable to "Priority Scan" on conventional systems. For P25 trunked systems, it is a whole new creature which is called "Priority ID Scan" and it is much different than conventional priority scanning. You can do Priority ID Scan without having the conventional "Priority Scan" turned on.
There are Motorola trunked radio systems that are NOT P25 systems. As Voyager mentioned, these systems can have certain channels established by the system administrator as priority channels. For you to use this, you would use a third type of priority setting, which is "Preemptive Priority ID Scanning". For this to function, you'd have to flag the channel on your scanner and that channel would have to be one of those system priority channels. However this is a little different that P25 priority.
Our local system is a P25 trunked system. I do use Priority ID Scan for this. Here are some of the things I've observed:
Several of my fire channels are flagged as priority channels. I can be holding on a silent police channel and if one of those priority fire channels becomes active, the scanner will "jump" to that fire channel. If there is a break in active transmissions on the police channel, such as between the time the officer calls the dispatcher and the dispatcher answers, a fire channel becomes active, it will "jump" to that priority fire channel.
