Post photos to facebook, if W & family are on it. She sees, you aren't pursuing. When I was on vacation, I had a summer vacation 2015 album, and then an summer vacation 2015 - extras for family album. W was included in both, but I was not just peppering her with pictures. She liked them all - even the ones that made it fairly clear that it was just me with the boys. Seemed a bit strange to me, but she thanked me.
If there is one that is something only she would really get and enjoy, them sure, that's your insider conspiratorial connection around your love of your kids. Otherwise, let everyone (or at least your whole family) see.
On the postcard, just get them talking about their feelings and how they're enjoying vacation? If they are thinking of their M, it will come out eventually. Then maybe ask if there is something that they would like to do re their mom? That keeps it about them, while still allowing them to keep a good connection with your W.
Me: 50 W:43 S6, S3 M: 12 yrs. T: 17 M is bad & Not happy Bomb Mar '14 S 5 Feb '15 D Bomb 13 Apr '15 (but "no hurry") DB Coach May '15 Wants proceed on D Aug '15 Starting 1-on-1 negotiations Sept '15