I spent a lot of the weekend writing letters. I was inspired to get out one of my typewriters for my responses, but I also had a number of postcards to return. Sometimes, depending on the model of the machine, you can get a postcard to feed through, but the portable I was using hates thicker papers. My solution is labels.
I use regular ol' white address labels all the time in my mail art. So instead of using them to make a blank space on an envelope, I just roll them through and type my message there. Two to three labels is the sweet spot for most regular sized postcards. You can affix them horizontally or vertically. I like to put a piece of paper over the typed labels before I rub them down to affix them to the card. That way, I don't smear the ink. More process pictures are available on Instagram.
Now, one Instagram commentor says that they were told at the counter by a clerk that postal regulations state that ANYTHING stuck on a postcard means it has to be sent at letter rate postage. This is one of those rules that I hem and haw on. I'll maintain that labels aren't stickers and risk it. I can't count how many postcards I've received with address labels affixed. Plus, I send handmade mixed media postcards all the time without problems. It's all part of the mailing fun.
If it's heavy or weird, I like to add extra postage, but some typed labels? I'll do the postcard rate. Of course, I ALWAYS put on my return address. They can send it back if they wish. That's why I love the blue mailbox, no judgement. And no misinformed clerks either, which has happened to me. My absolute favorite is when they pull out the guide for mailing and my pieces pass all their tests (because I have one of those guides in my house).