I'm starting to hand stamp and then handwrite thank you notes to photo editors and clients. We're all bombarded with digital correspondence now. And with the amount of snail mail I receive down, getting real mail is a little treat.
My sister and my insurance broker (yep!) are the best at this. Every year I receive a birthday and holiday card from them. Ok, normal. But both bring back little social graces. My sister sends thank you cards immediately. My broker, every once in a while, will send a little "check-in" card, sometimes around a minor holiday, sometimes not. But each time I feel a little special and think, wow they took the time to write a personalized note. Now my sister, being my sister, sends beautiful cards which ups the positive-feeling factor massively.
Top of mind, tip of tongue. That's what it's about.
Give it a try too and feel free to share any tweaks you've done with your marketing.