This is a definite yes. If the metal detector beeps, turn around and you'll see "QUOT" for quota if you've been selected for random screening.
I paid particular attention to this on a trip this weekend. The QUOT method was happening at LHR but in IST they had a triple beep and a strobing light. When selected for random check they didn't wand the person at all, but just took hand swabs. A small child was randomly selected and they just let him through without doing anything.
When the alarm went off for real, it was a single beep and a light indicated the location of the alarm. If it was at foot level, they'd tell you to take your shoes off and put them through the x-ray, otherwise they'd wand they'd perform a hand search.
So if you're particularly observant you can probably tell by the beep, but if you don't catch that, you'll have a second or two to turn around and see the alarm indicator - real/random.