if you feel like telling people to scan COVID-19 QR codes: don't.

instead, try: "if you see a COVID-19 QR code poster, remember to scan".

telling people to simply "scan, scan, scan" is unhelpful — it doesn't say how.

coaching people to scan in response to the poster as a cue is much more likely to encourage habit formation.

an if-this-then-that instruction is like a small computer program for the brain.

other variations which tie the specific desired behaviour to another:

"whenever you enter a place, look for the COVID-19 QR code and scan it".

"always check you have scanned the COVID-19 QR code before you leave a place".

I don't think "slip, slop, slap, scan" makes sense. you can't scan as soon as you slip-slop-slap (usually sunscreen requires you wait 15 minutes before going out too).

it might still work as, "slip, slop, slap, plan to scan". we want people to consciously form an intent to scan.

try to avoid shaming people, or implying shame or guilt, for failure to scan. we don't want people who happen to miss out on scanning for one reason or another, to react by changing their attitude by dismissing scanning altogether just to ease their feeling of shame/guilt.

instead of a message of shame/guilt for failure to scan, we can promote a failure-tolerant message like, "scan as much as you can". genuinely, that's what we need: enough people scanning enough of the time, i.e. not perfection.

if you want to model positive scanning by posting screenshots of your app diary, think again. a screenshot isn't the specific desired behaviour. if you feel up to it, consider posting videos of you actually scanning into places, which is the specific behaviour to imitate.

to scan, some people need a higher purpose. the Ministry hasn't explained it well — even the poster says, "scan" to "sign-in" to "stop the virus". this is confusing, vague and inaccurate. be ready to explain how scanning benefits contact tracing, the scanner and their community.

loss aversion is a powerful way to motivate behaviour. once we're clear on the benefits of scanning, see if you can present it as loss aversion:

"scan to make contact tracing faster".
"scan to save time during contact tracing".

when you find yourself writing a post like, "I went out and saw nobody scanning, so everyone should scan!", stop and rewrite it.

by repeating that you saw nobody scanning, you risk implicitly normalizing non-scanning.

instead, try describing how you specifically scanned (saw QR code, paused, remembered to scan).

or maybe positively highlight how at least one other person was scanning.

or emphasize that you scanned and did your bit, and now it's the reader's turn (i.e. reciprocity).