I already mentioned it but I love leaving drawings on peoples profiles on DeviantArt after they have favorited a work or started watching me. I don’t know. I just like showing them my appreciation when I can. I usually do about 1-2 a day depending on how many or how few favorites / new watches I get.
This is one that I did today. :) They had favorited my fan art of Jack Frost and started following me! So I left them with this along with a thank you (my thank yous usually look like FMDOFMOASDFMAOMFAOFMFA)