That is a use of PP that I had not hear of before. I do not think that I would use it in my game unless the person had PP active at the time of casting.
MDC
RM2's Spell User Companion has a section on magical flourishes that we use for this type of thing. Essentially Power Perception allows you to get a sense of power being used over space and time.
"There was a great ritual cast here centuries ago"
"You feel a tingle up your spine as magic is cast nearby."
It is a great resource and has led to more than on PC going completely mundane to avoid detection.
I use this part as well... you may not See the power with out actively concentrating, but if it is powerful enough, or you are sensitive enough, (developed your perception high enough) you might feel old energies, or even sense places of great power, or even feel some one using spells down the street.
MERP used this type of power sensing, warning that anytime power was used, it might attract unwanted attention, and at the same time, a Spell user had a chance to sense spell use nearby as well.