I live in Copenhagen, Denmark and I love snail mail. Any card will make me happy :D
You can write whatever you want on the postcards :) I just like getting them.
I do collect mail labels, like Airmail/Par Avion/Prioritaire/Priority etc.
I would love if you used some if your country has them.
I do also like if you need ideas:
-Mail box/Letter box/Anything postal related
-LGBT+ (can have nudity, it's fine)
-Mail art/Something Handmade
-Manga (including yaoi)
-90's (Backstreet boys, Nsync, Buffy, Fresh Prince, Spice Girls and so on)
-Poirot, Miss Marple, Sherlock Holmes
-Star wars/Star trek
-Condom ad cards
I don't mind ad cards if they fit one of the themes.
But again any cards are cool, I just think it's fun to get mail 🙂