Buying some stamp money is a way to say thanks. A way to show your love and appreciation for the things I make and share.
In my art practice I tend to post a lot of letters to people. In my performance work I often invite people to write themselves a letter and then send it to them in the mail at some time in the future. I love doing this, one day I put a little jar on my piano and said if people wanted to throw some stamp money in the jar to help me with the cost of envelopes and stamps that would be great. And people did! Now it's a thing.
Giving me some stamp money is a way to help fund everything I create. I really appreciate it.