Steps for detecting a zone should include:
seeing if a cutter is followed through a key (sometimes ill tell my players to switch on cutters as i want to keep my big guys near the key as often as possible)
Does the Defence rotate on ball reversals? (Zones will tend to get lazy on reversals and stay put after a few passes)
Is there a too much help on a drive? (man to man theres one maybe two help defenders depending on the offensive set, zones will collapse with 3 sometimes 4 help defenders)
Whats the offence doing? (If the offence isnt moving then the defence wont move, many a times ive heard coaches getting angry because it looks like im playing a zone when in reality, their offence is a 4 out 1 in with no off ball movement)
If i coach against what i think is a zone, ill get a court supervisor across and run a give and go on one side, before reversing the ball to the cutter and letting him/her drive to the bucket. In a loose motion offence set-up this is usually effective to expose a zone.