Loyalty schemes suck. They're another piece of plastic to cart around with you (more than one unless you're some kind of supermarket loyalist), and despite that fact that almost everybody uses them apparently they never remember to actually scan the cards, because every supermarket's automated checkout machine nags you about it. To save you the trouble of doing it yourself, I've ranked the big four in terms of tone and overall obnoxiousness on a 1-10 scale.
Tesco: "Scan your Clubcard to earn Clubcard points."
Great. Completely non-prescriptive. There is at least one way to earn Clubcard points, and that way is to scan your Clubcard. If you wish to earn Clubcard points, then you could do it by scanning your Clubcard. If you don't wish to earn Clubcard points, then do whatever the fuck you like. Tone is fairly matter-of-fact, perhaps a little sumptuous. The only thing better would be not saying anything at all. 9/10.
Sainsburys (new): "If you have a Nectar card, please scan it now."
Pretty good. A gentle reminder that doesn't impede your flow if you don't have a card. Loses points because you could have scanned your card at any time previously, and "now" is the last possible time, so the machine is assuming you've forgotten and/or is low-key advertising the scheme at you. Like Tesco, tone is neutral, though with a faint hint of the excitement to come if you actually do scan your card. 8/10.
M&S: "Scan your Sparks card and we'll donate to your chosen Sparks charity".
At first glance, very similar to Tesco, but worse because of the charity guilt trip. A far better way to donate to charity is just to, you know, donate to charity. You know we're here for the discounts, so cut the crap. Tone starts out okay, but it's such a boring and (relatively) long-winded sentence that it's hard to keep the lilt up all the way through. 6/10.
Waitrose: "Do you have myWaitrose card?"
A little pointed, given that you can scan your myWaitrose card at any time, and it makes you press "No" to confirm your guilt. How loyal are you, really? Are you even a myWaitrose member? Oh? Are you sure you didn't mean to go to the Tesco down the road? No idea of tone because it's displayed rather than spoken. 4/10.
Sainsburys (old): "Have you swiped your Nectar card?"
Terrible. Firstly, you know damn well I haven't. Secondly, if I forgot about it, I certainly don't want to be mocked by a machine. Given the fact that the machine already knows what you've done, it's impossible for it not to sound smarmy when it says this. M&S machines used to say a very similar thing. 0/10.