Sometimes I have fun writing letters. At my best, I had a box full of interesting paper, stickers, cool pens, and even a bronze seal with a stick of sealing wax to use it with. I need to make another one of those, because they are fun!
Sealing wax is neat stuff. It’s more pliable than candle wax, which will just break. You light the little wax “candle” and drip a blob onto your paper, or whatever you want to seal shut. As the wax is still soft, then you stamp it with your seal, which can even be a signet ring. I really wish I’d done a better job making my signet ring in college, I may have to make a stamp from Sculpey clay to replace it.
Of course, seals were often used by kings and nobles in medieval times onward, and are still occasionally used on official documents. It’s a fun way to lend an aura of regality to a letter or note. You can get seals and sealing wax at stationery stores, in all different colors. Look for something that looks like a small square candle, like this: