Induction loops are simple to spot - just look for the rectangles formed from buzz-saw cuts in the tarmac sealed with rubbery goop, into which the wires have been laid.
It's apparently an urban myth that they won't detect an aluminium bike - aluminium is conductive so will still trigger the detector.
Apaprently the best way to trigger these is to cycle along the saw-cut. If you (sensibly) take primary in the middle of the box, you are lease likely to induce the field and trip the switch. Also if the wire is laid in a "Z" shape across the road this is meant to detect 2-wheelers better. Basically, the further your wheels are from the wire of the loop, the less likely you are to trip the switch.
There's also an urban rumour that if you attach a high-power magnet to your shoe and put your foot down over one of the wire-cuts you're more likely to trigger the field.
At the last building where I worked, to open the security gates and barriers to get out of the basement car park you had to ride exactly across the intersection of the saw-cuts forming the rectangle. If you missed it, you had to loop back around and try again. My current building has a proximity detector in the ceiling, which is mounted in such a way as to be obscured by a roof support until you're just below it. If you approach too slow, you don't trigger it either.
I also think that the "flash your lights at the detector and it will think it's an ambulance and will change" advice is also an urban myth.
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