Using a strong pin is pretty annoying, and a relatively visible signal when using the phone on the street etc, So it can be a good filter(maybe via street cams) to filter suspicious people - which isn't a bad goal for law enforcement.

That sounds good until you remember the Bayesian Base Rate Fallacy: there are very few terrorists (the base rate of terrorism is very low), so filtering on "people with strong passphrases" is going to produce an overwhelming feed of false positives.

Be careful not to take the base rate fallacy too far, with enough difference in likelihood even a small base rate won't prevent an effect from being significant, and regardless of the base rate you'll still get some information out of it, it might just not be as much as you wanted.

Nobody cares that you're using an alphanumeric passcode on your iPhone.

Some corps require or strongly encourage it. My employer does.

And most parents I know use alphanumeric to keep their kids from wiping their phones and iPads just by tapping the numbers. (A four digit number code auto-submits on the 4th tap, so all it takes is 40 toddler taps. An alphanumeric code can be any length and won't submit unless the actual submit button is tapped.)

Corporate email profiles on BYOD phones often enforce a long passcode requirement, so you've got a lot of Fortune 500 sales guys to screen out if you're stopping and searching anybody with a suspiciously long password.

I'm at a loss as to how alphabet agency can determine a weak passcode vs strong passcode was used. how does a pin get stored on the phone? surely, not plain text of a 4 digit pin. if they do any encryption to the 4 digit pin, how would it appear any different than a significantly stronger passcode?

The grandparent post was about determining the complexity of a PIN/Passcode by watching it being entered - more screen interaction = more complex.

It uses a different screen. If you have a 4 digit pin, the entry screen looks a lot like the phone dialer, with the numbers 0-9.

If you have a stronger passcode, you see a full keyboard instead.

The prompt is different based on the type of code you use.

Except that with Touch ID, you only have to enter it when you reboot the phone, or if you've mis-swiped 5 times. I've had a strong pin for a couple of years, and really don't find it even a slight inconvenience (in the way that I use a super-weak password for Netflix, as entering passwords on an Apple TV is a real pain)

People who desire to be secure in their electronic papers and effects are not and should not be considered "suspicious people".